A citation is a standardized note that tells your reader exactly where you found a piece of information. It typically includes the author’s name, the title of the work, the date it was published, and where to find it. Citations appear in two places: a short reference inside your text (called an in-text citation or footnote) and a longer, detailed entry in a list at the end of your paper. The three most common citation styles are APA, MLA, and Chicago, and each formats these details differently.
The Two Parts of Every Citation
Every citation system uses a pair: a brief marker in the body of your writing and a full entry in a list at the end. The in-text marker gives just enough information for the reader to locate the full entry, which contains every detail needed to track down the original source.
In APA style, the in-text marker uses the author’s last name and year of publication, like (Jones, 1998). In MLA, it uses the author’s last name and a page number, like (Jones 42). In Chicago’s notes-and-bibliography system, you place a numbered footnote at the bottom of the page instead. All three styles require that every in-text marker has a matching full entry in the references, works cited, or bibliography at the end.
When you directly quote someone’s words, most styles ask you to include a page number so the reader can find the exact passage. When you paraphrase or refer to an entire work, a page number is usually optional in APA but still expected in MLA.
APA Style Examples
APA (American Psychological Association) style is widely used in psychology, education, nursing, and the social sciences. Its current edition is APA 7th edition. The in-text format follows an author-date pattern, and reference list entries use a specific order: author, date, title, and source.
Book
In-text: (Yu, 2020)
Reference list: Yu, C. (2020). Interior Chinatown. Pantheon Books.
Notice that only the first word of the book title is capitalized in the reference list. In APA, book titles are italicized and use what’s called “sentence case,” meaning you capitalize the first word and proper nouns only.
Website
In-text: (Mantel, 2025)
Reference list: Mantel, B. (2025, April 24). How to be a caregiver for someone with multiple sclerosis. AARP. https://www.aarp.org/caregiving/health/info-2025/multiple-sclerosis-care-plan/
For websites, APA asks for the most specific date available. If the page has no date at all, you write (n.d.) in place of the year. The site name appears after the title, and the entry ends with the URL. If the author and site name are the same (for example, an organization publishing on its own site), you skip the site name to avoid repeating it.
Website with an Organization as Author
In-text: (World Health Organization, 2018)
Reference list: World Health Organization. (2018, May 24). The top 10 causes of death. https://www.who.int/news-room/fact-sheets/detail/the-top-10-causes-of-death
MLA Style Examples
MLA (Modern Language Association) style is the standard in literature, writing, and the humanities. Its current edition is the 9th edition. MLA in-text citations use the author’s last name and a page number in parentheses, with no comma between them.
Book
In-text: (Yu 45)
Works cited: Yu, Charles. Interior Chinatown. Pantheon Books, 2020.
Unlike APA, MLA uses the author’s full name in the works cited entry and capitalizes major words in titles (called “title case”).
Citing Generative AI
MLA has published specific guidance for citing tools like ChatGPT. The key principle: do not list the AI as the author. Instead, describe the prompt you used as the title, name the AI tool as the container (the platform where the content lives), and specify the model version, publisher, and date you generated the output.
Works cited example: “Describe the theme of nature in Jane Austen’s Mansfield Park” prompt. ChatGPT, model GPT-4o, OpenAI, 23 Sept. 2024, chatgpt.com/share/66f1b0a0-d704-8000-be9a-85f53c850607.
If the AI tool provides a shareable link, include it. If it doesn’t, use the general URL for the tool. MLA also recommends that you track down and directly cite any secondary sources the AI references rather than relying on the AI’s summary alone, since AI tools don’t always cite sources accurately.
Chicago Style Examples
Chicago style is common in history, business, and the arts. It offers two systems. The notes-and-bibliography system uses numbered footnotes (or endnotes) paired with a bibliography, and it’s the more distinctive of the two. The other system, author-date, works similarly to APA.
In the notes-and-bibliography system, there are important formatting differences between the footnote and the bibliography entry. Footnotes list the author’s name in normal order (first name, last name), separate elements with commas, and include a specific page number. Bibliography entries invert the author’s name (last name, first name), separate elements with periods, and give the full page range for articles.
Book
Footnote: 1. Charles Yu, Interior Chinatown (Pantheon Books, 2020), 45.
Bibliography: Yu, Charles. Interior Chinatown. Pantheon Books, 2020.
When you cite the same source again later in the paper, Chicago lets you use a shortened footnote: 3. Yu, Interior Chinatown, 48.
Journal Article
Footnote: 1. Hyeyoung Kwon, “Inclusion Work: Children of Immigrants Claiming Membership in Everyday Life,” American Journal of Sociology 127, no. 6 (2022): 1842–43, https://doi.org/10.1086/720277.
Bibliography: Kwon, Hyeyoung. “Inclusion Work: Children of Immigrants Claiming Membership in Everyday Life.” American Journal of Sociology 127, no. 6 (2022): 1818–59. https://doi.org/10.1086/720277.
Notice that the footnote cites only pages 1842–43 (the specific pages referenced), while the bibliography gives the article’s full page range of 1818–59.
How to Choose the Right Style
Your instructor, publisher, or organization almost always specifies which style to use. If no one tells you, the general conventions are: APA for social sciences, education, and health fields; MLA for English, literature, and humanities; Chicago for history, business, and some of the arts. Many professional journals list their required citation style in their submission guidelines.
Whichever style you use, the rule that matters most is consistency. Mixing APA formatting in one citation with MLA formatting in another will confuse readers and cost you credibility. Pick one system and follow it throughout.
What Happens When Information Is Missing
Real sources don’t always provide every detail a citation template calls for. Each style has rules for handling gaps. In APA, a webpage with no publication date gets (n.d.) where the year would go. A source with no individual author can list the organization as the author. For direct quotes from sources without page numbers, you can reference a paragraph number, chapter, section heading, or another logical identifier instead.
The goal is always to give the reader enough information to find the original source. If a piece of information genuinely doesn’t exist (no author, no date, no page number), acknowledge the gap using whatever placeholder the style guide provides and include every other detail you can.