# Latex Bibliography Show All References

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For any academic/research writing, incorporating references into a document is an important task. Fortunately, LaTeX has a variety of features that make dealing with references much simpler, including built-in support for citing references. However, a much more powerful and flexible solution is achieved thanks to an auxiliary tool called BibTeX (which comes bundled as standard with LaTeX). Recently, BibTeX has been succeeded by BibLaTeX, a tool configurable within LaTeX syntax.

BibTeX provides for the storage of all references in an external, flat-file database. (BibLaTeX uses this same syntax.) This database can be referenced in any LaTeX document, and citations made to any record that is contained within the file. This is often more convenient than embedding them at the end of every document written; a centralized bibliography source can be linked to as many documents as desired (write once, read many!). Of course, bibliographies can be split over as many files as one wishes, so there can be a file containing sources concerning topic A () and another concerning topic B (). When writing about topic AB, both of these files can be linked into the document (perhaps in addition to sources specific to topic AB).

## Embedded system

If you are writing only one or two documents and aren't planning on writing more on the same subject for a long time, you might not want to waste time creating a database of references you are never going to use. In this case you should consider using the basic and simple bibliography support that is embedded within LaTeX.

LaTeX provides an environment called that you have to use where you want the bibliography; that usually means at the very end of your document, just before the command. Here is a practical example:

\begin{thebibliography}{9}\bibitem{lamport94} Leslie Lamport, \textit{\LaTeX: a document preparation system}, Addison Wesley, Massachusetts, 2nd edition, 1994. \end{thebibliography}

OK, so what is going on here? The first thing to notice is the establishment of the environment. is a keyword that tells LaTeX to recognize everything between the begin and end tags as data for the bibliography. The mandatory argument, which I supplied after the begin statement, is telling LaTeX how wide the item label will be when printed. Note however, that the number itself is not the parameter, but the number of digits is. Therefore, I am effectively telling LaTeX that I will only need reference labels of one character in length, which ultimately means no more than nine references in total. If you want more than nine, then input any two-digit number, such as '56' which allows up to 99 references.

Next is the actual reference entry itself. This is prefixed with the command. The cite_key should be a unique identifier for that particular reference, and is often some sort of mnemonic consisting of any sequence of letters, numbers and punctuation symbols (although not a comma). I often use the surname of the first author, followed by the last two digits of the year (hence lamport94). If that author has produced more than one reference for a given year, then I add letters after, 'a', 'b', etc. But, you should do whatever works for you. Everything after the key is the reference itself. You need to type it as you want it to be presented. I have put the different parts of the reference, such as author, title, etc., on different lines for readability. These linebreaks are ignored by LaTeX. The command formats the title properly in italics.

## Citations

To actually cite a given document is very easy. Go to the point where you want the citation to appear, and use the following: , where the cite_key is that of the bibitem you wish to cite. When LaTeX processes the document, the citation will be cross-referenced with the bibitems and replaced with the appropriate number citation. The advantage here, once again, is that LaTeX looks after the numbering for you. If it were totally manual, then adding or removing a reference would be a real chore, as you would have to re-number all the citations by hand.

Instead of WYSIWYG editors, typesetting systems like \TeX{} or \LaTeX{}\cite{lamport94} can be used.

### Referring more specifically

If you want to refer to a certain page, figure or theorem in a text book, you can use the arguments to the command:

\cite[chapter, p.~215]{citation01}

The argument, "p. 215", will show up inside the same brackets. Note the tilde in [p.~215], which replaces the end-of-sentence spacing with a non-breakable inter-word space. This non-breakable inter-word space is inserted because the end-of-sentence spacing would be too wide, and "p." should not be separated from the page number.

### Multiple citations

When a sequence of multiple citations is needed, you should use a single command. The citations are then separated by commas. Here's an example:

\cite{citation01,citation02,citation03}

The result will then be shown as citations inside the same brackets, depending on the citation style.

### Bibliography styles

There are several different ways to format lists of bibliographic references and the citations to them in the text. These are called citation styles, and consist of two parts: the format of the abbreviated citation (i.e. the marker that is inserted into the text to identify the entry in the list of references) and the format of the corresponding entry in the list of references, which includes full bibliographic details.

Abbreviated citations can be of two main types: numbered or textual. Numbered citations (also known as the Vancouver referencing system) are numbered consecutively in order of appearance in the text, and consist in Arabic numerals in parentheses (1), square brackets [1], superscript1, or a combination thereof[1]. Textual citations (also known as the Harvard referencing system) use the author surname and (usually) the year as the abbreviated form of the citation, which is normally fully (Smith 2008) or partially enclosed in parenthesis, as in Smith (2008). The latter form allows the citation to be integrated in the sentence it supports.

Below you can see three of the styles available with LaTeX:

Here are some more often used styles:

Style NameAuthor Name FormatReference FormatSorting
plainHomer Jay Simpson#ID#by author
unsrtHomer Jay Simpson#ID#as referenced
abbrvH. J. Simpson#ID#by author
alphaHomer Jay SimpsonSim95by author
abstractHomer Jay SimpsonSimpson-1995a
acmSimpson, H. J.#ID#
authordate1Simpson, Homer JaySimpson, 1995
apaciteSimpson, H. J. (1995)Simpson1995
namedHomer Jay SimpsonSimpson 1995

However, keep in mind that you will need to use the natbib package to use most of these.

### No cite

If you only want a reference to appear in the bibliography, but not where it is referenced in the main text, then the command can be used, for example:

Lamport showed in 1995 something... \nocite{lamport95}.

A special version of the command, , includes all entries from the database, whether they are referenced in the document or not.

### Natbib

Citation commandOutput

Goossens et al. (1993)
(Goossens et al., 1993)

Goossens, Mittlebach, and Samarin (1993)
(Goossens, Mittlebach, and Samarin, 1993)

Goossens et al.
Goossens, Mittlebach, and Samarin

1993
(1993)

Goossens et al. 1993
Goossens et al., 1993
(priv. comm.)

Using the standard LaTeX bibliography support, you will see that each reference is numbered and each citation corresponds to the numbers. The numeric style of citation is quite common in scientific writing. In other disciplines, the author-year style, e.g., (Roberts, 2003), such as Harvard is preferred. A discussion about which is best will not occur here, but a possible way to get such an output is by the package. In fact, it can supersede LaTeX's own citation commands, as Natbib allows the user to easily switch between Harvard or numeric.

The first job is to add the following to your preamble in order to get LaTeX to use the Natbib package:

\usepackage[options]{natbib}

Also, you need to change the bibliography style file to be used, so edit the appropriate line at the bottom of the file so that it reads: . Once done, it is basically a matter of altering the existing commands to display the type of citation you want.

StyleSourceDescription
plainnatProvidednatbib-compatible version of plain
abbrvnatProvidednatbib-compatible version of abbrv
unsrtnatProvidednatbib-compatible version of unsrt
apsrevREVTeX 4 home pagenatbib-compatible style for Physical Review journals
rmpapsREVTeX 4 home pagenatbib-compatible style for Review of Modern Physics journals
IEEEtranNTeX Catalogue entrynatbib-compatible style for IEEE publications
achemsoTeX Catalogue entrynatbib-compatible style for American Chemical Society journals
rscTeX Catalogue entrynatbib-compatible style for Royal Society of Chemistry journals

#### Customization

OptionMeaning
:  :  : Parentheses () (default), square brackets [], curly braces {} or angle brackets <>
: multiple citations are separated by semi-colons (default) or commas
:  : author year style citations (default), numeric citations or superscripted numeric citations
: multiple citations are sorted into the order in which they appear in the references section or also compressing multiple numeric citations where possible
the first citation of any reference will use the starred variant (full author list), subsequent citations will use the abbreviated et al. style
for use with the chapterbib package. redefines \thebibliography to issue \section* instead of \chapter*
keeps all the authors’ names in a citation on one line to fix some hyperref problems - causes overfull hboxes

The main commands simply add a t for 'textual' or p for 'parenthesized', to the basic command. You will also notice how Natbib by default will compress references with three or more authors to the more concise 1st surname et al version. By adding an asterisk (*), you can override this default and list all authors associated with that citation. There are some other specialized commands that Natbib supports, listed in the table here. Keep in mind that for instance does not support and will automatically choose between all authors and et al..

The final area that I wish to cover about Natbib is customizing its citation style. There is a command called that can be used to override the defaults and change certain settings. For example, I have put the following in the preamble:

\bibpunct{(}{)}{;}{a}{,}{,}

The command requires six mandatory parameters.

1. The symbol for the opening bracket.
2. The symbol for the closing bracket.
3. The symbol that appears between multiple citations.
4. This argument takes a letter:
• n - numerical style.
• s - numerical superscript style.
• any other letter - author-year style.
5. The punctuation to appear between the author and the year (in parenthetical case only).
6. The punctuation used between years, in multiple citations when there is a common author. e.g., (Chomsky 1956, 1957). If you want an extra space, then you need .

Some of the options controlled by are also accessible by passing options to the natbib package when it is loaded. These options also allow some other aspect of the bibliography to be controlled, and can be seen in the table (right).

So as you can see, this package is quite flexible, especially as you can easily switch between different citation styles by changing a single parameter. Do have a look at the Natbib manual, it's a short document and you can learn even more about how to use it.

## BibTeX

I have previously introduced the idea of embedding references at the end of the document, and then using the command to cite them within the text. In this tutorial, I want to do a little better than this method, as it's not as flexible as it could be. I will concentrate on using BibTeX.

A BibTeX database is stored as a .bib file. It is a plain text file, and so can be viewed and edited easily. The structure of the file is also quite simple. An example of a BibTeX entry:

@article{greenwade93,author="George D. Greenwade",title="The {C}omprehensive {T}ex {A}rchive {N}etwork ({CTAN})",year="1993",journal="TUGBoat",volume="14",number="3",pages="342--351"}

Each entry begins with the declaration of the reference type, in the form of . BibTeX knows of practically all types you can think of, common ones are: book, article, and for papers presented at conferences, there is inproceedings. In this example, I have referred to an article within a journal.

After the type, you must have a left curly brace '' to signify the beginning of the reference attributes. The first one follows immediately after the brace, which is the citation key, or the BibTeX key. This key must be unique for all entries in your bibliography. It is this identifier that you will use within your document to cross-reference it to this entry. It is up to you as to how you wish to label each reference, but there is a loose standard in which you use the author's surname, followed by the year of publication. This is the scheme that I use in this tutorial.

Next, it should be clear that what follows are the relevant fields and data for that particular reference. The field names on the left are BibTeX keywords. They are followed by an equals sign (=) where the value for that field is then placed. BibTeX expects you to explicitly label the beginning and end of each value. I personally use quotation marks ("), however, you also have the option of using curly braces ('{', '}'). But as you will soon see, curly braces have other roles, within attributes, so I prefer not to use them for this job as they can get more confusing. A notable exception is when you want to use characters with umlauts (ü, ö, etc), since their notation is in the format , and the quotation mark will close the one opening the field, causing an error in the parsing of the reference. Using in the preamble to the source file can get round this, as the accented characters can just be stored in the file without any need for special markup. This allows a consistent format to be kept throughout the file, avoiding the need to use braces when there are umlauts to consider.

Remember that each attribute must be followed by a comma to delimit one from another. You do not need to add a comma to the last attribute, since the closing brace will tell BibTeX that there are no more attributes for this entry, although you won't get an error if you do.

It can take a while to learn what the reference types are, and what fields each type has available (and which ones are required or optional, etc). So, look at this entry type reference and also this field reference for descriptions of all the fields. It may be worth bookmarking or printing these pages so that they are easily at hand when you need them. Much of the information contained therein is repeated in the following table for your convenience.

articlebookbookletinbookincollectioninproceedings ≈ conferencemanualmastersthesis, phdthesismiscproceedingstech reportunpublished
addressooooooooo
annote
author+*o++o+o++
booktitle++
chaptero
crossref
editionoooo
editor*ooo
howpublishedoo
institution+
journal+
key
monthoooooooooooo
noteooooooooooo+
numberooooooo
organizationooo
pagesooo
publisher+++oo
school+
seriesooooo
title++++++++o+++
typeoooo
volumeoooooo
year++o+++o+o++o

+ Required fields, o Optional fields

### Authors

BibTeX can be quite clever with names of authors. It can accept names in forename surname or surname, forename. I personally use the former, but remember that the order you input them (or any data within an entry for that matter) is customizable and so you can get BibTeX to manipulate the input and then output it however you like. If you use the forename surname method, then you must be careful with a few special names, where there are compound surnames, for example "John von Neumann". In this form, BibTeX assumes that the last word is the surname, and everything before is the forename, plus any middle names. You must therefore manually tell BibTeX to keep the 'von' and 'Neumann' together. This is achieved easily using curly braces. So the final result would be "John {von Neumann}". This is easily avoided with the surname, forename, since you have a comma to separate the surname from the forename.

Secondly, there is the issue of how to tell BibTeX when a reference has more than one author. This is very simply done by putting the keyword and in between every author. As we can see from another example:

@book{goossens93,author="Michel Goossens and Frank Mittelbach and Alexander Samarin",title="The LaTeX Companion",year="1993",publisher="Addison-Wesley",address="Reading, Massachusetts"}

This book has three authors, and each is separated as described. Of course, when BibTeX processes and outputs this, there will only be an 'and' between the penultimate and last authors, but within the .bib file, it needs the ands so that it can keep track of the individual authors.

### Standard templates

Be careful if you copy the following templates, the % sign is not valid to comment out lines in bibtex files. If you want to comment out a line, you have to put it outside the entry.

@article
An article from a magazine or a journal.
• Required fields: author, title, journal, year.
• Optional fields: volume, number, pages, month, note.
@article{Xarticle,author="",title="",journal="",%volume="",%number="",%pages="",year="XXXX",%month="",%note="",}
@book
A published book
• Required fields: author/editor, title, publisher, year.
• Optional fields: volume/number, series, address, edition, month, note.
@book{Xbook,author="",title="",publisher="",%volume="",%number="",%series="",%address="",%edition="",year="XXXX",%month="",%note="",}
@booklet
A bound work without a named publisher or sponsor.
• Required fields: title.
• Optional fields: author, howpublished, address, month, year, note.
@booklet{Xbooklet,%author="",title="",%howpublished="",%address="",%year="XXXX",%month="",%note="",}
@conference
Equal to inproceedings
• Required fields: author, title, booktitle, year.
• Optional fields: editor, volume/number, series, pages, address, month, organization, publisher, note.
@conference{Xconference,author="",title="",booktitle="",%editor="",%volume="",%number="",%series="",%pages="",%address="",year="XXXX",%month="",%publisher="",%note="",}
@inbook
A section of a book without its own title.
• Required fields: author/editor, title, chapter and/or pages, publisher, year.
• Optional fields: volume/number, series, type, address, edition, month, note.
@inbook{Xinbook,author="",editor="",title="",chapter="",pages="",publisher="",%volume="",%number="",%series="",%type="",%address="",%edition="",year="",%month="",%note="",}
@incollection
A section of a book having its own title.
• Required fields: author, title, booktitle, publisher, year.
• Optional fields: editor, volume/number, series, type, chapter, pages, address, edition, month, note.
@incollection{Xincollection,author="",title="",booktitle="",publisher="",%editor="",%volume="",%number="",%series="",%type="",%chapter="",%pages="",%address="",%edition="",year="",%month="",%note="",}
@inproceedings
An article in a conference proceedings.
• Required fields: author, title, booktitle, year.
• Optional fields: editor, volume/number, series, pages, address, month, organization, publisher, note.
@inproceedings{Xinproceedings,author="",title="",booktitle="",%editor="",%volume="",%number="",%series="",%pages="",%address="",%organization="",%publisher="",year="",%month="",%note="",}
@manual
Technical manual
• Required fields: title.
• Optional fields: author, organization, address, edition, month, year, note.
@manual{Xmanual,title="",%author="",%organization="",%address="",%edition="",year="",%month="",%note="",}
@mastersthesis
Master's thesis
• Required fields: author, title, school, year.
• Optional fields: type (eg. "diploma thesis"), address, month, note.
@mastersthesis{Xthesis,author="",title="",school="",%type="diplomathesis",%address="",year="XXXX",%month="",%note="",}
@misc
Template useful for other kinds of publication
• Required fields: none
• Optional fields: author, title, howpublished, month, year, note.
@misc{Xmisc,%author="",%title="",%howpublished="",%year="XXXX",%month="",%note="",}
@phdthesis
Ph.D. thesis
• Required fields: author, title, year, school.
• Optional fields: address, month, keywords, note.
@phdthesis{Xphdthesis,author="",title="",school="",%address="",year="",%month="",%keywords="",%note="",}
@proceedings
The proceedings of a conference.
• Required fields: title, year.
• Optional fields: editor, volume/number, series, address, month, organization, publisher, note.
@proceedings{Xproceedings,title="",%editor="",%volume="",%number="",%series="",%address="",%organization="",%publisher="",year="",%month="",%note="",}
@techreport
Technical report from educational, commercial or standardization institution.
• Required fields: author, title, institution, year.
• Optional fields: type, number, address, month, note.
@techreport{Xtreport,author="",title="",institution="",%type="",%number="",%address="",year="XXXX",%month="",%note="",}
@unpublished
An unpublished article, book, thesis, etc.
• Required fields: author, title, note.
• Optional fields: month, year.
@unpublished{Xunpublished,author="",title="",%year="",%month="",note="",}

### Non-standard templates

@patent
BibTeX entries can be exported from Google Patents.
(see Cite Patents with Bibtex for an alternative)
@collection
@electronic
@Unpublished
For citing arXiv.org papers in a REVTEX-style article
(see REVTEX Author's guide)

### Preserving case of letters

In the event that BibTeX has been set by the chosen style not to preserve all capitalization within titles, problems can occur, especially if you are referring to proper nouns, or acronyms. To tell BibTeX to keep them, use the good old curly braces around the letter in question, (or letters, if it's an acronym) and all will be well! It is even possible that lower-case letters may need to be preserved - for example if a chemical formula is used in a style that sets a title in all caps or small caps, or if "pH" is to be used in a style that capitalises all first letters.

However, avoid putting the whole title in curly braces, as it will look odd if a different capitalization format is used:

For convenience though, many people simply put double curly braces, which may help when writing scientific articles for different magazines, conferences with different BibTex styles that do sometimes keep and sometimes not keep the capital letters:

As an alternative, try other BibTex styles or modify the existing. The approach of putting only relevant text in curly brackets is the most feasible if using a template under the control of a publisher, such as for journal submissions. Using curly braces around single letters is also to be avoided if possible, as it may mess up the kerning, especially with biblatex,[1] so the first step should generally be to enclose single words in braces.

### A few additional examples

Below you will find a few additional examples of bibliography entries. The first one covers the case of multiple authors in the Surname, Firstname format, and the second one deals with the incollection case.

@article{AbedonHymanThomas2003,author="Abedon, S. T. and Hyman, P. and Thomas, C.",year="2003",title="Experimental examination of bacteriophage latent-period evolution as a response to bacterial availability",journal="Applied and Environmental Microbiology",volume="69",pages="7499--7506"}@incollection{Abedon1994,author="Abedon, S. T.",title="Lysis and the interaction between free phages and infected cells",pages="397--405",booktitle="Molecular biology of bacteriophage T4",editor="Karam, Jim D. Karam and Drake, John W. and Kreuzer, Kenneth N. and Mosig, Gisela and Hall, Dwight and Eiserling, Frederick A. and Black, Lindsay W. and Kutter, Elizabeth and Carlson, Karin and Miller, Eric S. and Spicer, Eleanor",publisher="ASM Press, Washington DC",year="1994"}

If you have to cite a website you can use @misc, for example:

@misc{website:fermentas-lambda,author="Fermentas Inc.",title="Phage Lambda: description \& restriction map",month="November",year="2008",url="http://www.fermentas.com/techinfo/nucleicacids/maplambda.htm"}

The note field comes in handy if you need to add unstructured information, for example that the corresponding issue of the journal has yet to appear:

@article{blackholes,author="Rabbert Klein",title="Black Holes and Their Relation to Hiding Eggs",journal="Theoretical Easter Physics",publisher="Eggs Ltd.",year="2010",note="(to appear)"}

### Getting current LaTeX document to use your .bib file

At the end of your LaTeX file (that is, after the content, but before ), you need to place the following commands:

\bibliographystyle{plain}\bibliography{sample1,sample2,...,samplen}% Note the lack of whitespace between the commas and the next bib file.

Bibliography styles are files recognized by BibTeX that tell it how to format the information stored in the file when processed for output. And so the first command listed above is declaring which style file to use. The style file in this instance is (which comes as standard with BibTeX). You do not need to add the .bst extension when using this command, as it is assumed. Despite its name, the plain style does a pretty good job (look at the output of this tutorial to see what I mean).

The second command is the one that actually specifies the file you wish to use. The ones I created for this tutorial were called , , . . ., , but once again, you don't include the file extension. At the moment, the file is in the same directory as the LaTeX document too. However, if your .bib file was elsewhere (which makes sense if you intend to maintain a centralized database of references for all your research), you need to specify the path as well, e.g or (if the file is in the parent directory of the document that calls it).

Now that LaTeX and BibTeX know where to look for the appropriate files, actually citing the references is fairly trivial. The is the command you need, making sure that the ref_key corresponds exactly to one of the entries in the .bib file. If you wish to cite more than one reference at the same time, do the following: .

### Why won't LaTeX generate any output?

The addition of BibTeX adds extra complexity for the processing of the source to the desired output. This is largely hidden from the user, but because of all the complexity of the referencing of citations from your source LaTeX file to the database entries in another file, you actually need multiple passes to accomplish the task. This means you have to run LaTeX a number of times. Each pass will perform a particular task until it has managed to resolve all the citation references. Here's what you need to type (into command line):

(Extensions are optional, if you put them note that the bibtex command takes the AUX file as input.)

After the first LaTeX run, you will see errors such as:

LaTeX Warning: Citation `lamport94' on page 1 undefined on input line 21. ... LaTeX Warning: There were undefined references.

The next step is to run bibtex on that same LaTeX source (or more precisely the corresponding AUX file, however not on the actual .bib file) to then define all the references within that document. You should see output like the following:

This is BibTeX, Version 0.99c (Web2C 7.3.1) The top-level auxiliary file: latex_source_code.aux The style file: plain.bst Database file #1: sample.bib

The third step, which is invoking LaTeX for the second time will see more errors like "". Don't be alarmed, it's almost complete. As you can guess, all you have to do is follow its instructions, and run LaTeX for the third time, and the document will be output as expected, without further problems.

If you want a pdf output instead of a dvi output you can use instead of as follows:

(Extensions are optional, if you put them note that the bibtex command takes the AUX file as input.)

Note that if you are editing your source in vim and attempt to use command mode and the current file shortcut (%) to process the document like this:

You will get an error similar to this:

It appears that the file extension is included by default when the current file command (%) is executed. To process your document from within vim, you must explicitly name the file without the file extension for bibtex to work, as is shown below:

1. (without file extension, it looks for the AUX file as mentioned above)

However, it is much easier to install the Vim-LaTeX plugin from here. This allows you to simply type \ll when not in insert mode, and all the appropriate commands are automatically executed to compile the document. Vim-LaTeX even detects how many times it has to run pdflatex, and whether or not it has to run bibtex. This is just one of the many nice features of Vim-LaTeX, you can read the excellent Beginner's Tutorial for more about the many clever shortcuts Vim-LaTeX provides.

Another option exists if you are running Unix/Linux or any other platform where you have make. Then you can simply create a Makefile and use vim's make command or use make in shell. The Makefile would then look like this:

latex_source_code.pdf: latex_source_code.tex latex_source_code.bib pdflatex latex_source_code.tex bibtex latex_source_code.aux pdflatex latex_source_code.tex pdflatex latex_source_code.tex

### Including URLs in bibliography

As you can see, there is no field for URLs. One possibility is to include Internet addresses in field of or field of , , :

Note the usage of command to ensure proper appearance of URLs.

Another way is to use special field and make bibliography style recognise it.

You need to use in the first case or in the second case.

Styles provided by Natbib (see below) handle this field, other styles can be modified using urlbst program. Modifications of three standard styles (plain, abbrv and alpha) are provided with urlbst.

If you need more help about URLs in bibliography, visit FAQ of UK List of TeX.

### Customizing bibliography appearance

One of the main advantages of BibTeX, especially for people who write many research papers, is the ability to customize your bibliography to suit the requirements of a given publication. You will notice how different publications tend to have their own style of formatting references, to which authors must adhere if they want their manuscripts published. In fact, established journals and conference organizers often will have created their own bibliography style (.bst file) for those users of BibTeX, to do all the hard work for you.

It can achieve this because of the nature of the .bib database, where all the information about your references is stored in a structured format, but nothing about style. This is a common theme in LaTeX in general, where it tries as much as possible to keep content and presentation separate.

A bibliography style file () will tell LaTeX how to format each attribute, what order to put them in, what punctuation to use in between particular attributes etc. Unfortunately, creating such a style by hand is not a trivial task. Which is why (also known as custom-bib) is the tool we need.

can be used to automatically generate a .bst file based on your needs. It is very simple, and actually asks you a series of questions about your preferences. Once complete, it will then output the appropriate style file for you to use.

It should be installed with the LaTeX distribution (otherwise, you can download it) and it's very simple to initiate. At the command line, type:

latex makebst

LaTeX will find the relevant file and the questioning process will begin. You will have to answer quite a few (although, note that the default answers are pretty sensible), which means it would be impractical to go through an example in this tutorial. However, it is fairly straight-forward. And if you require further guidance, then there is a comprehensive manual available. I'd recommend experimenting with it and seeing what the results are when applied to a LaTeX document.

If you are using a custom built .bst file, it is important that LaTeX can find it! So, make sure it's in the same directory as the LaTeX source file, unless you are using one of the standard style files (such as plain or plainnat, that come bundled with LaTeX - these will be automatically found in the directories that they are installed. Also, make sure the name of the file you want to use is reflected in the command (but don't include the extension!).

### Localizing bibliography appearance

When writing documents in languages other than English, you may find it desirable to adapt the appearance of your bibliography to the document language. This concerns words such as editors, and, or in as well as a proper typographic layout. The package can be used here. For example, to layout the bibliography in German, add the following to the header:

\usepackage[fixlanguage]{babelbib}\selectbiblanguage{german}

Alternatively, you can layout each bibliography entry according to the language of the cited document:

The language of an entry is specified as an additional field in the BibTeX entry:

@article{mueller08,%...language={german}}

For to take effect, a bibliography style supported by it - one of , , , , , and - must be used:

\bibliographystyle{babplain}\bibliography{sample}

### Showing unused items

Usually LaTeX only displays the entries which are referred to with . It's possible to make uncited entries visible:

\nocite{Name89}% Show Bibliography entry of Name89\nocite{*}% Show all Bib-entries

### Getting bibliographic data

Many online databases provide bibliographic data in BibTeX-Format, making it easy to build your own database. For example, Google Scholar offers the option to return properly formatted output, which can also be turned on in the settings page.

One should be alert to the fact that bibliographic databases are frequently the product of several generations of automatic processing, and so the resulting BibTex code is prone to a variety of minor errors, especially in older entries.

### Helpful tools

See also: w:en:Comparison of reference management software
• BibDesk BibDesk is a bibliographic reference manager for Mac OS X. It features a very usable user interface and provides a number of features like smart folders based on keywords and live tex display.
• BibSonomy — A free social bookmark and publication management system based on BibTeX.
• BibTeXSearch BibTeXSearch is a free searchable BibTeX database spanning millions of academic records.
• Bibtex Editor - An online BibTeX entry generator and bibliography management system. Possible to import and export Bibtex files.
• Bibwiki Bibwiki is a Specialpage for MediaWiki to manage BibTeX bibliographies. It offers a straightforward way to import and export bibliographic records.
• cb2Bib The cb2Bib is a tool for rapidly extracting unformatted, or unstandardized bibliographic references from email alerts, journal Web pages, and PDF files.
• Citavi Commercial software (with size-limited free demo version) which even searches libraries for citations and keeps all your knowledge in a database. Export of the database to all kinds of formats is possible. Works together with MS Word and Open Office Writer. Moreover plug ins for browsers and Acrobat Reader exist to automatically include references to your project.
• CiteULike CiteULike is a free online service to organise academic papers. It can export citations in BibTeX format, and can "scrape" BibTeX data from many popular websites.

## Creating and Managing Bibliographies with BibTeX on Overleaf

By Lian Tze Lim

## Introduction

Many tutorials have been written about what $$\mathrm{Bib\TeX}$$ is and how to use it. However, based on my experience of providing support to Overleaf’s users, it’s still one of the topics that many newcomers to $$\mathrm{\LaTeX}$$ find complicated—especially when things don’t go quite right; for example: citations aren’t appearing; problems with authors’ names; not sorted to a required order; URLs not displayed in the references list, and so forth.

In this first article, one of a planned series to address references, we’ll pull together all the threads relating to citations, references and bibliographies, as well as how Overleaf and related tools can help users manage these.

We’ll start with a quick recap of how $$\mathrm{Bib\TeX}$$ and bibliography database () files work and look at some ways to prepare files. This is, of course, running the risk of repeating some of the material contained in many online tutorials, but future blog posts will expand our coverage to include bibliography styles and —the alternative package and bibliography processor.

## Bibliography: just a list of

Let’s first take a quick look “under the hood” to see what a $$\mathrm{\LaTeX}$$ reference list is comprised of—please don’t start coding your reference list like this because later in this article we’ll look at other, more convenient, ways to do this.

A reference list really just a list of :

By default, this environment is a numbered list with labels , and so forth. If the document class used is , automatically inserts a numberless section heading with (default value: References). If the document class is or report, then a numberless chapter heading with (default value: Bibliography) is inserted instead. Each takes a cite key as its parameter, which you can use with commands, followed by information about the reference entry itself. So if you now write

together with the block from before, this is what gets rendered into your PDF when you run a $$\mathrm{\LaTeX}$$ processor (i.e. any of , , or ) on your source file:

Figure 1: Citing entries from a list.

Notice how each is automatically numbered, and how then inserts the corresponding numerical label.

takes a numerical argument: the widest label expected in the list. In this example we only have two entries, so is enough. If you have more than ten entries, though, you may notice that the numerical labels in the list start to get misaligned:

Figure 2: with a label that’s too short.

We’ll have to make it instead, so that the longest label is wide enough to accommodate the longer labels, like this:

Figure 3: with a longer label width.

If you compile this example code snippet on a local computer you may notice that after the first time you run (or another $$\mathrm{\LaTeX}$$ processor), the reference list appears in the PDF as expected, but the commands just show up as question marks [?].

This is because after the first $$\mathrm{\LaTeX}$$ run the cite keys from each (, ) are written to the file and are not yet available for reading by the commands. Only on the second run of are the commands able to look up each cite key from the file and insert the corresponding labels (, ) into the output.

On Overleaf, though, you don’t have to worry about re-running yourself. This is because Overleaf uses the build tool, which automatically re-runs (and some other processors) for the requisite number of times needed to resolve outputs. This also accounts for other cross-referencing commands, such as and .

### A note on compilation times

Processing $$\mathrm{\LaTeX}$$ reference lists or other forms of cross-referencing, such as indexes, requires multiple runs of software—including the $$\mathrm{\TeX}$$ engine (e.g., ) and associated programs such as $$\mathrm{Bib\TeX}$$, , etc. As mentioned above, Overleaf handles all of these mulitple runs automatically, so you don’t have to worry about them. As a consequence, when the preview on Overleaf is refreshing for documents with bibliographies (or other cross-referencing), or for documents with large image files (as discussed separately here), these essential compilation steps may sometimes make the preview refresh appear to take longer than on your own machine. We do, of course, aim to keep it as short as possible! If you feel your document is taking longer to compile than you’d expect, here are some further tips that may help.

## Enter $$\mathrm{Bib\TeX}$$

There are, of course, some inconveniences with manually preparing the list:

• It’s up to you to accurately format each based on the reference style you’re asked to use—which bits should be in bold or italic? Should the year come immediately after the authors, or at the end of the entry? Given names first, or last names first?
• If you’re writing for a reference style which requires the reference list to be sorted by the last names of first authors, you’ll need to sort the s yourself.
• For different manuscripts or documents that use different reference styles you’ll need to rewrite the for each reference.

This is where $$\mathrm{Bib\TeX}$$ and bibliography database files ( files) are extremely useful, and this is the recommended approach to manage citations and references in most journals and theses. The approach, which is slightly different and gaining popularity, also requires a file but we’ll talk about in a future post.

Instead of formatting cited reference entries in a list, we maintain a bibliography database file (let’s name it for our example) which contains format-independent information about our references. So our file may look like this:

You can find more information about other $$\mathrm{Bib\TeX}$$ reference entry types and fields here—there’s a huge table showing which fields are supported for which entry types. We’ll talk more about how to prepare files in a later section.

Now we can use with the cite keys as before, but now we replace with a to choose the reference style, as well as to point $$\mathrm{Bib\TeX}$$ at the file where the cited references should be looked-up.

This is processed with the following sequence of commands, assuming our $$\mathrm{\LaTeX}$$ document is in a file named (and that we are using ):

and we get the following output:

Figure 4: $$\mathrm{Bib\TeX}$$ output using the bibliography style.

Whoah! What’s going on here and why are all those (repeated) processes required? Well, here’s what happens.

1. During the first run, all sees is a and a from . It doesn’t know what all the commands are about! Consequently, within the output PDF, all the commands are simply rendered as [?], and no reference list appears, for now. But writes information about the bibliography style and file, as well as all occurrences of , to the file .

2. It’s actually that $$\mathrm{Bib\TeX}$$ is interested in! It notes the file indicated by , then looks up all the entries with keys that match the commands used in the file. $$\mathrm{Bib\TeX}$$ then uses the style specified with to format the cited entries, and writes a formatted list into the file . The production of the file is all that’s achieved in this step; no changes are made to the output PDF.

3. When is run again, it now sees that a file is available! So it inserts the contents of i.e. the into the $$\mathrm{\LaTeX}$$ source, where is. After this step, the reference list appears in the output PDF formatted according to the chosen , but the in-text citations are still [?].

4. is run again, and this time the commands are replaced with the corresponding numerical labels in the output PDF!

As before, the build tool takes care of triggering and re-running and as necessary, so you don’t have to worry about this bit. You can inspect the generated file on Overleaf, if you click on the downward-pointing triangle next to the “Download as ZIP” button, and choose the “For submission (with .bbl)” option. This is also useful for some journal submission sites where their internal $$\mathrm{\LaTeX}$$ compilation systems do not run separately.

On some other journals, if you are asked to “copy the contents of the file into your manuscript”, you can also use this download option to access the file. You can then copy-and-paste the contents to replace the original lines in your manuscript.

A few further things to note about using $$\mathrm{Bib\TeX}$$ and :

• You may have noticed that although contained five $$\mathrm{Bib\TeX}$$ reference entries, only two are included in the reference list in the output PDF. This is an important point about $$\mathrm{Bib\TeX}$$: the file’s role is to store bibliographic records, and only entries that have been cited (via ) in the files will appear in the reference list. This is similar to how only cited items from an EndNote database will be displayed in the reference list in a Microsoft Word document. If you do want to include all entries—to be displayed but without actually citing all of them—you can write . This also means you can reuse the same file for all your $$\mathrm{\LaTeX}$$ projects: entries that are not cited in a particular manuscript or report will be excluded from the reference list in that document.
• $$\mathrm{Bib\TeX}$$ requires one and one to function correctly—in future posts we’ll see how to create multiple bibliographies in the same document. If you keep getting “undefined citation” warnings, check that you have indeed included those two commands, and that the names are spelled correctly. File extensions are not usually required, but bear in mind that file names are case sensitive on some operating systems—including on Overleaf! Therefore, if you typed (note the typo: “e”) instead of , or wrote when the actual file name is , you’ll get the dreaded [?] as citations.
• In the same vein, treat your cite keys as case-sensitive, always. Use the exact same case or spelling in your as in your file.
• The order of references in the file does not have any effect on how the reference list is ordered in the output PDF: the sorting order of the reference list is determined by the. For example, some readers might have noticed that, within my earlier example, the first citation in the text is numbered [2], while the second citation in the text () is numbered [1]! Have $$\mathrm{\LaTeX}$$ and $$\mathrm{Bib\TeX}$$ lost the plot? Not at all: this is actually because the style sorts the reference list by alphabetical order of the first author’s last name. If you prefer a scheme where the numerical citation labels are numbered sequentially throughout the text, you’ll have to choose a bibliography style which implements this. For example, if instead we had used for that example, we’d get the following output. Notice also how the formatting of each cited item in the reference list has automatically updated to suit the IEEE’s style:

Figure 5: bibliography style output.

We’ll talk more about different bibliography styles, including author–year citation schemes, in a future blog post. For now, let’s turn our attention to file contents, and how we can make the task of preparing files a bit easier.

## Taking another look at files

As you may have noticed earlier, a file contains $$\mathrm{Bib\TeX}$$ bibliography entries that start with an entry type prefixed with an . Each entry has a some key–value $$\mathrm{Bib\TeX}$$ fields, placed within a pair of braces (). The cite key is the first piece of information given within these braces, and every field in the entry must be separated by a comma:

As a general rule, every bibliography entry should have an , and field, no matter what the type is. There are about a dozen entry types although some bibliography styles may recognise/define more; however, it is likely that you will most frequently use the following entry types:

• for journal articles (see example above).
• for conference proceeding articles:
• for books (see examples above).
• , for dissertations and theses:
• is for a book chapter where the entire book was written by the same author(s): the chapter of interest is identified by a chapter number:
• is for a contributed chapter in a book, so would have its own and . The actual title of the entire book is given in the field; it is likely that an field will also be present:
• is for whatever doesn’t quite fit any other entry type. It can be especially useful for web pages—by writing or :
• you will often find it useful to add or in your files’ preamble (for more robust handling of URLs);
• not all bibliography styles support the field: doesn’t, but does. All styles support . More on this in a future post;
• you should be mindful that even web pages and entries should have an , a and a field:

### Multiple authors in $$\mathrm{Bib\TeX}$$

In a file, commas are only used to separate the last name from the first name of an author—if the last name is written first. Individual author names are separated by . So these are correct:

or

But none of the following will work correctly—you’ll get weird output, or even error messages from $$\mathrm{Bib\TeX}$$! So take extra care if you are copying author names from a paper or from a web page.

### Multiple-word last names

If an author’s last name is made up of multiple words separated by spaces, or if it’s actually an organisation, place an extra pair of braces around the last name so that $$\mathrm{Bib\TeX}$$ will recognise the grouped words as the last name:

Alternatively, you can use the format; some users find that clearer and more readable:

Remember: Whether the first or last name appears first in the output (“John Doe” vs “Doe, John”), or whether the first name is automatically abbreviated “J. Doe” or “Doe, J.” vs “John Doe” “J. Doe”), all such details are controlled by the .

is actually not a comment character in files! So, inserting a in files not only fails to comment out the line, it also causes some $$\mathrm{Bib\TeX}$$ errors. To get $$\mathrm{Bib\TeX}$$ to ignore a particular field we just need to rename the field to something that $$\mathrm{Bib\TeX}$$ doesn’t recognise. For example, if you want to keep a field around but prefer that it’s ignored (perhaps because you want $$\mathrm{Bib\TeX}$$ to use the field instead) write or the more human-readable .

To get $$\mathrm{Bib\TeX}$$ to ignore an entire entry you can remove the before the entry type. A valid reference entry always starts with a followed by the entry type; without the character $$\mathrm{Bib\TeX}$$ skips the lines until it encounters another .

## How/where do I actually get those files?

### Edit the file as plain text

Because files are plain text you can certainly write them by hand—once you’re familiar with $$\mathrm{Bib\TeX}$$’s required syntax. Just make sure that you save it with a extension, and that your editor doesn’t surreptitiously add a or some other suffix. On Overleaf you can click on the “Files…” link at the top of the file list panel, and then on “Add blank file” to create a fresh file to work on.

Pro tip: Did you know that Google Scholar search results can be exported to a $$\mathrm{Bib\TeX}$$ entry? Click on the “Cite” link below each search result, and then on the “$$\mathrm{Bib\TeX}$$” option search. You can then copy the $$\mathrm{Bib\TeX}$$ entry generated. Here’s a video that demonstrates the process. Note that you should always double-check the fields presented in the entry, as the automatically populated information isn’t always comprehensive or accurate!

### Help from GUI-based editors

Many users prefer to use a dedicated $$\mathrm{Bib\TeX}$$ bibliography database editor/manager, such as JabRef or BibDesk to maintain, edit and add entries to their files. Using a GUI can indeed help reduce syntax and spelling errors whilst creating bibliography entries in a $$\mathrm{Bib\TeX}$$ file. If you prefer, you can prepare your file on your own machine using JabRef, BibDesk or another utility, and then upload it to your Overleaf project using “Files > Bibliography > Upload .bib file”.

Pro tip: If you’d like to use the same for multiple Overleaf projects, have a look at this help article to set up a “master project”, or this one for sharing files from Google Drive (the instructions apply to other cloud-based storage solutions, such as Dropbox).

### Export from reference library services

If you click on the “Files > Bibliography” menu item in your Overleaf editor you may notice some options: Import your Mendeley, Zotero and CiteULike libraries! If you’re already using one of those reference library management services, Overleaf can now hook into the Web exporter APIs provided by those services to import the file (generated from your library) into your Overleaf project.

For other reference library services that don’t have a public API, or are not yet directly integrated with Overleaf, such as EndNote or Paperpile, look for an “export to ” option in the application or service. Once you have a file, you can then add it to your Overleaf project using the steps explained earlier and in the linked help articles.

### I’ve already got a reference list in a Microsoft Word/HTML/PDF file; can I somehow reuse the data without re-typing everything?

It used to be that you would have to hand-code each line into a or an entry (or another entry type) in a file. As you can imagine, it’s not exactly a task that many people look forward to. Fortunately, these days some tools are available to help. They typically take a plain text file, e.g.

and attempt to parse the lines, converting it into a structured bibliography as a $$\mathrm{Bib\TeX}$$ file. For example, have a look at text2bib or Edifix. Be sure to go through the options of these tools carefully, so that they work well with your existing unstructured bibliography in plain text.

## Summary and future articles

We’ve now had a quick look at how $$\mathrm{Bib\TeX}$$ processes a bibliography database file to resolve commands and produce a formatted reference list, as well as how to prepare files. In an forthcoming post we’ll look further into some popular options, as well as some citation niceties provided by the package.

Until then, happy $$\mathrm{Bib\TeX}$$ing!

More news from Overleaf

Lian Tze Lim

Community TeXpert

Computer scientist, once-lecturer, trainer. Enjoys tinkering with LaTeX in the name of productive procrastination (ahem). Personal motto: "all research students are insane at one time or another".

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