Chicago-style source citations come in two varieties: (1) notes and bibliography and (2) author-date.
"The notes and bibliography system is preferred by many working in the humanities—including literature, history, and the arts. In this system, sources are cited in numbered footnotes or endnotes. Each note corresponds to a raised (superscript) number in the text. Sources are also usually listed in a separate bibliography. The notes and bibliography system can accommodate a wide variety of sources, including unusual ones that don’t fit neatly into the author-date system.
The author-date system is more common in the sciences and social sciences. In this system, sources are briefly cited in the text, usually in parentheses, by the author’s last name and year of publication. Each in-text citation matches up with an entry in a reference list, where full bibliographic information is provided.
Aside from the use of numbered notes versus parenthetical references in the text, the two systems share a similar style. Follow the links at the top of this page to see examples of some of the more common source types cited in both systems.
Most authors choose the system used by others in their field or required by their publisher. Students who are unsure of which system to use will find more information here.