Historians generally use the Chicago Manual of Style or its derivative, A Manual for Writers of Term Papers, Theses, and Dissertations (commonly known as Turabian, after its author). Though not identical, the two styles are very similar. The Chicago/Turabian style offers two systems: 1) notes and bibliography (humanities style); 2) author-date. 

Historians prefer the humanities style because it accommodates a wide variety of sources. Documentation is presented by notes (either footnotes or endnotes) and a bibliography. 

Find copies of these manuals in the library

• After using a source, put a superscript number at the end of your sentence:

Marius notes that "history and writing are inseparable."³

• Cite the source in a correspondingly numbered note at the end of the page (footnote) or at the end of your paper (endnote):

3. Richard Marius. A Short Guide to Writing about History, 3rd ed. (New York: Longman, 1999), 5.

• If you use this source again, subsequent notes are shorter:

9. Marius, 105.

• In your bibliography, list the source alphabetically according to the author's last name:

Marius, Richard. A Short Guide to Writing about History, 3rd ed. New York: Longman, 1999.

Be aware of small differences across similar formats. For example:

• Book citations vary slightly for edited collections, multiple authors, translations, or new editions.
• Articles have subtle differences if they are newspapers, weekly magazines, or scholarly journals.