The Chicago Manual of Stylesource citations come in two varieties: (1) notes and bibliography and (2) author-date. The difference between the two often depends on subject matter and nature of sources cited, as each system is favored by different groups of scholars.
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.
Theauthor-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 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.