BibTeX-files may contain four different types of entries:

• @STRING defines abbreviations in the form of
  

  @string { foo = "Mrs. Foo" } 
  

  which can later be used in a tag like this

  author = foo # " and Mr. Bar" 
  

• @PREAMBLE defines how special text should be formatted.
• @COMMENT for comments not taken in regard by BibTeX.
• Entries each declaring a single reference to a type of publication, for example:@article, @book, @inproceedings etc.

A BibTeX entry consists of the type (the word after @), a citation-key and a number of tags which define various characteristics of the specific BibTeX entry.

Among those tags can be for example: author, title, year, etc. Some tags are mandatory for certain types of BibTeX entries, some are optional.

There is a set of standard-tags existing, which can be interpreted by BibTeX or third-party tools. Those which are unknown are ignored by BibTeX, thus can be used to store additional information without interfering with the final outcome of a document.

@misc{ patashnik-bibtexing,
       author = "Oren Patashnik",
       title = "BIBTEXing",
       year = "1988" }

A BibTeX tag is specified by its name followed by an equals-sign and the content. The tag's name is not case-sensitive. The content needs to be enclosed by either curly braces or quotation-marks. Which form of enclosure is used is depending on the user's taste, and both can be applied together in a single BibTeX entry, but there is one difference between those two methods: When quotation-marks are used, string concatenation using # is possible, but not when braces are used.

For example, the following statements are equal:

Title = {{Bib}\TeX} 
Title = "{Bib}\TeX" 
Title = "{Bib}" # "\TeX" 

It is important to know that abbreviations previously defined using the @string command can only be used in conjunction with other strings using the string concatenation.

@string{btx = "{\textsc{Bib}\TeX}"} 
Title = btx # "ing" 

Numbers can either be enclosed by braces or quotation-marks, but can stand alone. Tags are separated by commas; if not, the BibTeX parser will produce an error. The last tag can be finished with a comma, although not necessarily.

@article{mrx05, 
auTHor = "Mr. X", 
Title = {Something Great}, 
publisher = "nob" # "ody", 
YEAR = 2005, 
} 

is a correct BibTeX entry.