Bibliography management tools integrated to a document production system (such as EndNote/Word, or BibTeX/LaTeX) can automatically yield the presentation of references in documents. They can do it according to diverse bibliographic styles.
A bibliographic style matches (in the e-world) the presentation rules of the bibliographic references in the paper world.
Available bibliographic styles are numerous (there are hundreds of them), because each journal use its own presentation rules. So, EndNote proposes 300 bibliographic styles, and allows to define new ones. Bibliographic styles are often only slight modifications of base styles (less numerous). In the domain of computer science, one base style is plain from BibTeX. EndNote lists 19 domains in which styles are a priori different (agriculture, anthropology, biology, chemical, pharmacology, physics, psychology, public health, sciences, sociology, virology, etc.).
The following "figure" shows a unique reference printed according to three different styles (in that order): plain, apalike, and acm. This three styles are more or less distant. The printed version of reference is called physical version, on the opposite to its logical version.
Figure: the same reference, printed in bibliographic styles plain, apalike, and acm.
 S. H. Joseph and T. P. Pridmore. Knowledge-directed interpretation of mechanical engineering drawings. IEEE Transactions on PAMI, 14(9):211-222, September 1992.
[Joseph and Pridmore, 1992] Joseph, S. H. and Pridmore, T. P. (1992). Knowledge-directed interpretation of mechanical engineering drawings. IEEE Transactions on PAMI, 14(9):211-222.
 JOSEPH, S. H., and PRIDMORE, T. P. Knowledge-directed interpretation of mechanical engineering drawings. IEEE Transactions on PAMI 14, 9 (September 1992), 211-222.
Bibliographic style acts on:
- presence (or not) of an identification key in a specific format (numeric, alphabetic, etc.). Here, the apalike style (second in the figure) have a key containing the names of all the authors, followed by the year.
- order of the fields. For example, the year field generally found at the end, appears after the author field in the apalike style, and between parentheses before the pages in acm.
- separators: in this reference, year and number are surrounded by parentheses or not. Generally, we call separator all sequence of characters or font change located between two fields.
- typographic style of the fields: in the bibliographic style acm, authors are in small capitals, and the conference name (booktitle) in italics.
- presence (or not) of some fields, like month that does not appear in the apalike style, or like abstract and keywords, that never appear in the figure.
- fields format: in the author field, first and last name can be inverted (acm, apalike); for acm, a comma is before the and separating the two authors (that happens generally only when there are more than two authors).
Fields' presentation changes when they belong to a certain reference type. For example, the title field of a book is in italics, but in inproceedings, it is not.