Citing (A How-to Guide): Chicago Style 18th Edition

Chicago-style source citations come in two varieties: (1) notes and bibliography and (2) author-date.

In the notes and bibliography 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, Chicago’s oldest and most flexible, can accommodate a wide variety of sources, including unusual ones that don’t fit neatly into the author-date system.

In the author-date system, sources are briefly cited in the text, usually in parentheses, by 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. Because it credits researchers by name directly in the text while at the same time emphasizing the date of each source, the author-date system is preferred by many in the sciences and social sciences.

-- Chicago-Style Citation Quick Guide