When you summarise or paraphrase an idea from a source, or when you use a direct quote from a source, you must cite the author or body responsible for the work in a footnote. Each footnote should use a new number, even for a previously cited source. Most word processing software have a built-in footnote function, which will do the numbering and formatting automatically.
The footnote number should be placed at the end of the sentence or the end of a clause in a sentence, after any punctuation.
In the footnote you are required to provide full bibliographic details of the source the first time you cite the source; you can then use a shortened version of the author's name and title of the book in subsequent citations. See the tabs for different resources types for specific examples of how to do this.
The abbreviation ibid., previously used in Chicago when a citation duplicates the immediately preceding citation, is discouraged in favour of shortened citations.
The abbreviation op. cit., which is used in some referencing styles, is not used in the Chicago Style and should not be used in your assignments.
There can be times in your research when you have read the same idea from different authors in different sources. When including multiple authors in a footnote you should order them alphabetically according to the first author's surname and separating each citation with a semi-colon.
When a note contains not only the source of a fact or quotation in the text but related comments as well, the source comes first. A period usually separates the citation from the commentary. Such comments as "emphasis mine" are usually put in parentheses.
3 Shakespeare, Julius Caesar, act 3, sc. 1. Caesar's claim of constancy should be taken with a grain of salt.
4 Little, "Norms of Collegiality," 330 (my italics).
When a note includes a quotation, the source normally follows the terminal punctuation of the quotation. The entire source need not be put in parentheses, which involves changing existing parentheses to brackets and creating unnecessary clutter.
Some notes of commentary may require citations of their own. When a source is needed, it can be provided the same way as the example above (that is, providing a full footnote citation after a full stop) or, if the source has already been cited in full, it can be cited parenthetically.
Keep in mind that although Footnotes, Endnotes or Appendices are not counted in your formal word count, their word count should not exceed 25% of the word limit. This includes both citations as well as supplementary information.