Chicago and APA are two of the most widely used academic citation systems, but they serve different disciplines and operate on fundamentally different logic. Choosing the wrong one — or mixing rules from both — is a common error that affects the credibility of academic work. This guide breaks down the key differences across every major dimension.
Who Uses Each Style
| Style | Primary fields | Governing body |
|---|---|---|
| APA (7th ed.) | Psychology, social sciences, education, nursing, business | American Psychological Association |
| Chicago (17th ed.) | History, humanities, arts, literature, some social sciences | University of Chicago Press |
Two Systems Within Chicago
Chicago has two distinct citation systems — a detail many students miss:
| Chicago system | In-text format | End-of-text format | Common in |
|---|---|---|---|
| Notes-Bibliography (NB) | Footnotes or endnotes with full citation details | Bibliography | Humanities: history, literature, arts |
| Author-Date (AD) | (Author year, page) | Reference list | Sciences and social sciences |
The Author-Date system is structurally similar to APA. The Notes-Bibliography system is not — it uses numbered footnotes instead of parenthetical citations.
In-Text Citation Comparison
| Situation | APA | Chicago Author-Date | Chicago Notes-Bibliography |
|---|---|---|---|
| Single author | (Smith, 2022) | (Smith 2022) | ¹ John Smith, Title (Publisher, 2022), 45. |
| Two authors | (Smith & Jones, 2022) | (Smith and Jones 2022) | ¹ Smith and Jones, 2022, 45. |
| Three or more | (Smith et al., 2022) | (Smith et al. 2022) | ¹ Smith et al., 2022, 45. |
| With page number | (Smith, 2022, p. 45) | (Smith 2022, 45) | Included in footnote |
Key difference: APA uses a comma between author and year; Chicago Author-Date does not. APA uses «&» between two authors; Chicago uses «and.»
Reference List vs. Bibliography
| Feature | APA Reference List | Chicago Bibliography |
|---|---|---|
| Title | «References» | «Bibliography» or «Works Cited» |
| What’s included | Only sources cited in the text | May include sources consulted but not cited |
| Author format | Last, F. M. (inverted for all) | Last, First (inverted for first author only in NB) |
| Date position | After author, in parentheses | At the end of the entry (NB) or after author (AD) |
| Indentation | Hanging indent | Hanging indent |
Journal Article: Format Comparison
APA 7th edition
Smith, J. A. (2022). Memory consolidation during sleep in young adults. Journal of Cognitive Neuroscience, 34(5), 912–928. https://doi.org/10.1162/jocn_a_01830Chicago Notes-Bibliography
Smith, John A. "Memory Consolidation During Sleep in Young Adults." Journal of Cognitive Neuroscience 34, no. 5 (2022): 912–928. https://doi.org/10.1162/jocn_a_01830Chicago Author-Date
Smith, John A. 2022. "Memory consolidation during sleep in young adults." Journal of Cognitive Neuroscience 34 (5): 912–928. https://doi.org/10.1162/jocn_a_01830Book: Format Comparison
| Feature | APA | Chicago NB |
|---|---|---|
| Title format | Sentence case, italicized | Title case, italicized |
| Publisher location | Not required (removed in 7th ed.) | Required: City: Publisher |
| Edition | (3rd ed.) | 3rd ed. |
Other Key Differences
| Feature | APA | Chicago |
|---|---|---|
| Running head | Required for manuscripts; optional for student papers | Not used |
| Abstract | Required for most papers | Not standard |
| Footnotes | Content notes only (not citations) | Primary citation method in NB system |
| Ibid. | Not used | Used in NB to refer to the immediately preceding source |
| DOI format | https://doi.org/… | https://doi.org/… |
Which One Should You Use?
The choice is almost always made for you by your discipline, institution, or target journal. If your department or professor has not specified a style, check what the leading journals in your field use. History and humanities departments typically require Chicago NB. Psychology and social science programs almost always require APA. When in doubt, ask before you write — changing citation styles mid-document is time-consuming.
For full APA formatting guidance, see the APA format center.