MLA, APA, Chicago, the short version.

Which one do I use?

• MLA, literature, languages, humanities. If you're writing about a novel, a poem, a film, or anything in an English department: MLA.
• APA, social sciences, education, psychology, nursing. Anything with data and participants.
• Chicago / Turabian, history, some humanities. Chicago has two flavors: notes-bibliography (humanities) and author-date (sciences).

When in doubt, check the assignment sheet. When still in doubt, ask your instructor. The formats differ in small ways that get you docked points.

MLA 9, in-text and Works Cited.

In-text: (Author Page). For example: (Morrison 47).

Works Cited, book:

Morrison, Toni. Beloved. Knopf, 1987.

Works Cited, journal article:

Smith, Jane. "Title of Article." Journal Name, vol. 12, no. 3, 2024, pp. 45–67.

Works Cited, web source:

Author Last, First. "Title." Site Name, Date, URL.

APA 7, in-text and References.

In-text: (Author, Year) or (Author, Year, p. X) for direct quotes. For example: (Morrison, 1987) or (Smith, 2024, p. 47).

References, book:

Morrison, T. (1987). Beloved. Knopf.

References, journal article:

Smith, J. (2024). Title of article. Journal Name, 12(3), 45–67. https://doi.org/xx.xxxx/xxxxx

References, web source:

Author Last, F. (Year, Month Day). Title of article. Site Name. URL

Chicago 17, notes & bibliography.

Footnote (first reference):

1. Toni Morrison, Beloved (New York: Knopf, 1987), 47.

Footnote (subsequent):

2. Morrison, Beloved, 52.

Bibliography entry:

Morrison, Toni. Beloved. New York: Knopf, 1987.

Edge cases students actually hit.

• No author listed? MLA and APA: use the article title in the in-text. Chicago: use title in the note.
• Two authors? MLA: (Smith and Jones 47). APA: (Smith & Jones, 2024). Chicago: "Smith and Jones."
• Three or more authors? All three use "et al." after the first author. MLA requires "and" before the final author only if listing all; APA allows "et al." from the first citation.
• AI-generated text? MLA 9 recommends citing ChatGPT-style outputs as a source with the prompt and the date. APA 7 treats it as a software tool. Chicago 17 requires a footnote with the tool, version, and date.

Citing Social Media and Ephemeral Content Across Citation Styles

Social media citations have evolved significantly across all three major citation styles as platforms have become primary sources for academic research. MLA 9 requires the author's real name (if known) followed by their username in parentheses, the full text of short posts or the first 20 words of longer ones, the platform name in italics, the date posted, and the URL. For example, a tweet would appear as: Smith, John (@johnsmith). "Climate data reveals significant trends." Twitter, 15 Mar. 2023, twitter.com/johnsmith/status/123456. The format prioritizes accessibility and assumes that social media posts function as standalone publications rather than contributions to larger works.

APA 7 treats social media as personal communications when content is not archived or accessible to general readers, requiring in-text citations only without reference list entries. However, publicly accessible posts from professional accounts or verified users require full references including the author's username in brackets, the exact date with month and day, the first 20 words of the post followed by bracketed description of any multimedia elements, the platform name, and the URL. Chicago 17 offers flexibility between notes-bibliography and author-date systems. In notes-bibliography, a footnote includes the author's name, the platform, the post date, and the URL. The manual acknowledges that ephemeral content poses archival challenges and recommends researchers screenshot time-sensitive material.

Edge cases present particular challenges across all three systems. Content from private accounts, deleted posts, or platforms requiring authentication raises questions about verifiability and reader access. MLA recommends citing unavailable sources only when essential and noting access restrictions. APA distinguishes between recoverable archived content and truly ephemeral material, while Chicago suggests including access dates for volatile content. Stories, reels, and temporary posts that disappear after 24 hours should be treated as personal communications in APA or cited with explicit notation of their temporary nature in MLA and Chicago. Researchers should maintain personal archives of cited ephemeral content to support scholarly integrity even when public access becomes impossible.

Recent Changes to Digital Object Identifiers and URL Formatting

The treatment of DOIs and URLs underwent substantial revision in recent editions of all three citation styles, reflecting the digital transformation of scholarly communication. MLA 9 introduced a significant shift by making DOIs and URLs optional for works that readers can locate through database searches or other means. When included, MLA now requires only the domain name and path without the protocol (http:// or https://), resulting in cleaner citations such as doi.org/10.1234/example rather than https://doi.org/10.1234/example. This change recognizes that modern browsers automatically interpret addresses regardless of protocol specification. However, MLA still requires full URLs for sources that would be difficult to locate otherwise, such as independent websites, institutional repositories, or subscription databases where the specific URL provides necessary access information.

APA 7 made DOIs mandatory when available for journal articles and other scholarly sources, positioning them as the preferred permanent identifier over URLs. The format changed from the older "doi:" prefix to the current hyperlink format using doi.org/ as the domain. For sources without DOIs, APA now requires URLs without "Retrieved from" phrasing unless the source material is designed to change over time (such as Wikipedia entries or regularly updated reports). APA also eliminated the requirement to include database names for most sources, reasoning that DOIs provide sufficient retrieval information. The manual specifies that URLs and DOIs should be live hyperlinks in electronic submissions but should not include periods at the end to avoid confusion about whether the punctuation forms part of the address.

Chicago 17 maintains the most conservative approach by continuing to require access information for most electronic sources while allowing flexibility based on the source type. The manual recommends DOIs over URLs when both are available and accepts either the older doi: format or the newer https://doi.org/ format, though it expresses preference for consistency within a single work. For stable content from well-known databases, Chicago permits omission of URLs if the source can be easily located through title and database name searches. However, for working papers, preprints, institutional repositories, and independent websites, Chicago requires full URLs. The style also uniquely recommends including access dates for sources likely to change or disappear, particularly news websites, organizational pages, and social media. This practice acknowledges that digital sources may be updated or removed, and the access date provides context for which version the researcher consulted.

Handling Preprints, Data Sets, and Non-Traditional Research Outputs

Preprints and data sets have become central to research dissemination, yet citation standards for these materials developed slowly relative to their increasing prevalence. MLA 9 treats preprints as articles but requires identification of the preprint server in the container position where a journal name would typically appear. For instance, a bioRxiv preprint citation includes the author, article title in quotation marks, bioRxiv in italics as the container, the submission or revision date, and the DOI. The format assumes that preprints function as standalone scholarly works with intellectual authority comparable to published articles, though researchers may note version numbers when relevant. MLA's container system accommodates preprints naturally because the style already conceptualizes sources as nested within larger platforms or publications.

APA 7 introduced specific guidelines for preprints in response to their proliferation in psychology, medicine, and related fields. The reference format includes bracketed notation indicating [Preprint] immediately after the title to distinguish unpublished material from peer-reviewed articles. When preprints later receive journal publication, researchers should cite the published version rather than the preprint to direct readers to the final, peer-reviewed content. For data sets, APA requires the author or contributor name (which may be an organization), the publication year, the data set title in italics, version number in brackets if applicable, the repository or publisher name, and the DOI or URL. The format treats data sets as standalone works rather than supplementary materials, reflecting their growing status as citable research outputs with independent intellectual value.

Chicago 17 provides accommodation for preprints, data sets, and other non-traditional outputs through flexible application of its core citation principles rather than prescriptive formats for each type. The manual recommends adapting the closest comparable format and adding clarifying information as needed. For preprints, this typically means following article format while specifying the preprint server and noting the draft status or version number. Data sets should include contributor names, publication or release date, title, version or edition, repository name, and persistent identifier. Chicago particularly emphasizes the importance of version numbers for computational notebooks, software code, and iterative data releases where multiple versions coexist and differ substantially. The style also addresses conference presentations, posters, and presentation slides as increasingly archived and accessible research outputs. These materials should include presenter names, presentation titles, conference names and locations, presentation dates, and URLs or repository information when available through platforms such as Figshare, Zenodo, or institutional repositories.