Citing your sources means giving credit to the original author or creator whenever you use someone else’s words, ideas, or data. Every citation has two parts: a short reference in the body of your text (called an in-text citation) and a full entry in a list at the end of your paper. The exact format depends on the citation style your class, journal, or publisher requires.
Pick the Right Citation Style
Three citation styles cover the vast majority of academic and professional writing. Your instructor or publisher will usually tell you which one to use, but if they don’t, the convention in your field is the default:
- APA (American Psychological Association) is the standard in psychology, education, and the social sciences. It uses an author-date system for in-text citations.
- MLA (Modern Language Association) is used in literature, arts, and the humanities. It uses an author-page number system for in-text citations.
- Chicago is most common in history and some humanities disciplines. It offers both a footnote/endnote system and an author-date system, depending on the publisher’s preference.
If you’re writing for a law course, you’ll likely use Bluebook style, which has its own footnote format. For most other assignments, one of the three styles above will apply.
Know When You Need a Citation
You need to cite a source any time you quote someone’s exact words, paraphrase their argument, or use a specific fact, statistic, or idea that isn’t common knowledge. Common knowledge is information so widely accepted that you can find it stated, without a source, in at least five credible places. “The Earth orbits the Sun” doesn’t need a citation. A specific statistic about global temperatures from a NASA report does.
The practical rule, as Purdue’s Online Writing Lab puts it: when in doubt, just cite. If the citation turns out to be unnecessary, an instructor will tell you. An unnecessary citation is a minor formatting issue. A missing citation can be treated as plagiarism.
The Two Parts of Every Citation
Regardless of style, your citation system has two connected pieces. Understanding this structure makes every style guide easier to follow.
In-Text Citations
These are the brief markers inside your sentences or at the end of them. In APA, an in-text citation includes the author’s last name and the year of publication, like (Smith, 2023). In MLA, it includes the author’s last name and the page number, like (Smith 47). In Chicago’s footnote system, you place a superscript number that points to a footnote at the bottom of the page.
A few rules apply across styles. Each in-text citation must match exactly one entry in your reference list. The year in your in-text citation should match the year in the full entry. If a work has no date, use “n.d.” in APA or follow your style guide’s equivalent convention. If a work has no named author, use a shortened version of the title in place of the author’s name.
The Reference List
At the end of your paper, you include a full list of every source you cited. APA calls this “References,” MLA calls it “Works Cited,” and Chicago calls it a “Bibliography.” Each entry gives your reader enough information to find the original source: the author, publication date, title of the work, and where to find it (a publisher, journal name, URL, or DOI).
Entries are alphabetized by the first author’s last name. If a source has no author, it’s alphabetized by its title. Every in-text citation in your paper needs a corresponding entry here, and every entry here should be cited somewhere in your paper.
What Goes Into a Full Citation
The exact order and punctuation vary by style, but nearly every citation collects the same core information. Before you start writing, gather these details for each source:
- Author: The person or organization responsible for the content. When no individual is credited, use the organization’s name.
- Date: The year of publication, or the most specific date available. For a webpage, use the date it was published or last updated (not “last reviewed,” since a review doesn’t necessarily change the content).
- Title: The title of the article, chapter, or webpage, plus the title of the larger work it appears in (the journal, book, or website).
- Source location: For print works, this is the publisher name or journal volume and page numbers. For online sources, this is the URL or DOI (a permanent digital link assigned to many journal articles).
Here’s what a webpage citation looks like in APA format:
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
Notice the organization is the author, the date is as specific as possible, the title is italicized, and the URL closes out the entry. If this page’s content changed over time and wasn’t archived, you’d add a retrieval date: “Retrieved January 9, 2025, from [URL].”
Citing Websites and Online Sources
Web sources follow the same logic as print sources but require a few extra decisions. When the author of a webpage is the same as the website name, omit the site name to avoid repetition. When a page lists an individual author, use their name and include the site name as part of the source element.
For example, an article on AARP’s website written by a named journalist would look like this in APA:
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/
If no date appears on the page at all, use “(n.d.)” in place of the year. If the page is a live data tool (like a population counter) that changes constantly, include a retrieval date so your reader knows what version of the data you saw.
Citing Generative AI
If you use output from tools like ChatGPT, DALL-E, or similar AI models, most style guides now have specific rules. MLA’s updated guidance is a good example of how the field is handling this.
In MLA style, you do not list the AI tool as the author. Instead, your citation starts with a description of what was generated, often including your prompt. The AI tool’s name goes in the container position (the way a journal title would), followed by the specific model version, the company that made the tool, the date you generated the content, and a URL if one is available.
An MLA works-cited entry for a ChatGPT response looks like this:
“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 linked to outside sources in its response, cite those original sources directly rather than citing the AI’s summary of them. Treating the AI as a middleman and going straight to the primary source is stronger for your credibility and easier for your reader to verify.
Formatting Tips That Save Time
Citation managers like Zotero, Mendeley, or the built-in tool in Google Docs can automatically generate citations in your chosen style. They aren’t perfect, so always double-check the output against your style guide, but they handle the tedious formatting (italics, punctuation, hanging indents) and keep your reference list organized as your paper grows.
If you’re formatting by hand, pay attention to the details that differ between styles. APA uses a hanging indent (the first line is flush left, subsequent lines are indented), and so does MLA. APA italicizes journal titles and volume numbers. MLA italicizes container titles but not volume numbers. These small differences matter because instructors and editors notice them, and consistency signals that your work is careful and trustworthy.
When you’re unsure about an unusual source type, like a podcast episode, a social media post, or a government dataset, search your style guide’s official website for that specific format. The APA Style site and MLA Style Center both maintain searchable databases of example citations covering dozens of source types.