Entry types

When entering a reference in the bibliography database, the first thing to decide is what type of entry it is. No fixed classification scheme can be complete, but BibTeX provides enough entry types to handle almost any reference reasonably well.

References to different types of publications contain different information; a reference to a journal might include the volume and number of the journal, which is usually not meaningful for a book. Therefore, database entries of different types have different fields for each entry type, the fields are divided into three classes:

omitting the field will produce an error message and may result in a badly formatted bibliography entry. If the required information is not meaningful, you are using the wrong entry type.
the field's information will be used if present, but can be omitted without causing any formatting problems. A reference should contain any available information that might help the reader, so you should include the optional field if it is applicable.
the field is ignored. BibTeX ignores any field that is not required or optional, so you can include any fields you want in a bibliography entry. It's often a good idea to put all relevant information about a reference in its bibliography entry - even information that may never appear in the bibliography. For example, if you want to keep an abstract of a paper in a computer file, put it in an 'abstract' field in the paper's bibliography entry. The bibliography database file is likely to be as good a place as any for the abstract, and it is possible to design a bibliography style for printing selected abstracts.

BibTeX ignores the case of letters in the entry type.