The Chicago Manual of Style, 17th Edition by 
Student's Guide to Writing College Papers, Fifth Edition by 
A Manual for Writers of Research Papers, Theses, and Dissertations, Ninth Edition by The Author-Date Chicago-style citation system is primarily used in the sciences and social sciences. This system employs parenthetical references in-text and a reference list at the end of the document. You can use the Chicago Manual of Style's Author-Date Quick Guide to get started on citing with this system.
Elements of the Author-Date system:
Reference List
A separate reference list is included at the end of a Chicago style publication. In reference list citations, the author's last name comes first. The year of publication comes after the author's name, which is different from Notes-Bibliography system. Citations are punctuated by periods instead of commas, and the full page range is cited. The bibliography itself is alphabetically sorted by authors' last name.
In-Text Citation
In-text citations are included in the body of a Chicago-style Author-Date system publication, directly after the passage or sentence referring to the the cited materials. In-text citations are in parenthesis and include the author's last name, year of publication (not divided by a comma), and the page number of the citation (if applicable), i.e. (Valdez 2021, 56).
For additional paper formatting information, refer to the Chicago Manual of Style. Additionally, the Purdue OWL Author-Date Sample Paper is also a helpful resource.
