A citation identifies the source of an idea, fact, or quotation so your reader can find it. Every citation contains the same basic ingredients: the author’s name, the date of publication, the title of the work, and where it can be found. The exact order, punctuation, and formatting of those ingredients depend on which citation style you’re using.
The Core Pieces of Every Citation
Regardless of style, you need to collect the same information before you can write a citation. For a book, that means the author, publication year, title, publisher, and edition if applicable. For a journal article, you need the author, year, article title, journal name, volume number, issue number, and page range. For an online source, you need a URL or DOI (a permanent digital link assigned to scholarly articles) in addition to the standard details.
Before you start formatting, gather all of this information from the source itself. Check the title page of a book rather than the cover, since they sometimes differ. For websites, note the exact URL and the date you accessed it if the content could change. For journal articles, look for a DOI, which is more reliable than a URL because it never changes even if the publisher moves the article.
Choosing a Citation Style
Your instructor, publisher, or organization will tell you which style to use. The three most common are APA, MLA, and Chicago. APA is standard in the social sciences, education, and nursing. MLA is used in the humanities, especially English and literature courses. Chicago appears in history, some business writing, and many book-length publications.
Each style arranges the same information differently. Here’s how all three handle the same journal article:
- APA: Frank, H. (2011). Wolves, Dogs, Rearing and Reinforcement: Complex Interactions Underlying Species Differences in Training and Problem-Solving Performance. Behavior Genetics, 41(6), 830-839.
- MLA: Frank, H. “Wolves, Dogs, Rearing and Reinforcement: Complex Interactions Underlying Species Differences in Training and Problem-Solving Performance.” Behavior Genetics 41.6 (2011): 830-39. Print.
- Chicago: Frank, H. 2011. “Wolves, Dogs, Rearing and Reinforcement: Complex Interactions Underlying Species Differences in Training and Problem-Solving Performance.” Behavior Genetics 41 (6):830-839.
Notice the differences. APA puts the year right after the author’s name in parentheses. MLA places it near the end. Chicago uses a period after the year instead of parentheses. APA italicizes the journal title and volume number together. MLA puts the article title in quotation marks and uses a period-separated volume and issue format. These details matter because consistency within one style is what makes your citations correct.
In-Text Citations vs. Reference Lists
Most citation styles require two components: a short reference inside your text (the in-text citation) and a full entry on a separate page at the end of your paper (the reference list, works cited, or bibliography, depending on the style). Every in-text citation must match an entry in your reference list, and every entry in your reference list should correspond to something you actually cited in your paper.
In APA, in-text citations come in two forms. A parenthetical citation places the author and year at the end of a sentence: “Falsely balanced news coverage can distort the public’s perception of expert consensus on an issue (Koehler, 2016).” A narrative citation works the author’s name into the sentence itself: “Koehler (2016) noted the dangers of falsely balanced news coverage.” Both point to the same full entry on your reference page.
MLA uses a similar parenthetical approach but includes the author’s last name and the page number rather than the year: (Koehler 42). Chicago gives you a choice between footnotes and parenthetical author-date citations, depending on which variant your instructor requires.
How to Cite a Book
Books are the most straightforward source to cite. In APA format, a book citation follows this pattern: Author last name, first initial. (Year). Title of book. Publisher. If the book has a DOI, add it at the end. For example:
Smith, J. (2020). The economics of everyday decisions. Oxford University Press.
In MLA, the same book would look like: Smith, John. The Economics of Everyday Decisions. Oxford University Press, 2020. Notice that MLA uses the author’s full first name, capitalizes all major words in the title, and puts the year at the end rather than after the author.
For books with two authors, list both names. For books with three or more authors, APA lists up to 20 before using an ellipsis, while MLA lists only the first author followed by “et al.” after three or more. These details vary by style, so keep a style guide handy for your first few papers.
How to Cite a Website or Online Article
Websites require you to include enough information for a reader to find the exact page you referenced. In APA, a basic website citation looks like: Author last name, first initial. (Year, Month Day). Title of page. Site Name. URL. If there is no identifiable author, start with the title. If there is no date, use “n.d.” in place of the year.
The trickiest part of citing websites is identifying the author. Look for a byline, an “About” page, or the organization responsible for the content. A government agency or nonprofit can serve as the author when no individual is named. If you genuinely cannot identify who created the content, that may be a sign the source isn’t reliable enough to cite in the first place.
How to Cite AI-Generated Content
If you use a generative AI tool like ChatGPT or Gemini in your work, you need to cite it. APA provides specific guidance for this. The author is the company that developed the tool (OpenAI for ChatGPT, Google for Gemini), not the AI itself. AI cannot be listed as an author.
For citing the tool generally, include the company name, the year the tool was last updated, the name of the tool in italics followed by a bracketed description like “[Large language model],” and the URL. For citing a specific chat conversation, use the date the chat occurred, give the chat a descriptive title in italics followed by “[Generative AI chat],” and provide the URL of the chat along with the name of the AI tool. Consider editing your chat’s title within the tool to something descriptive before you create the reference, since many tools auto-generate vague titles.
Formatting Your Reference List
Your reference list goes on a new page at the end of your paper. In APA, title it “References.” In MLA, title it “Works Cited.” In Chicago’s bibliography variant, title it “Bibliography.” All three styles alphabetize entries by the first author’s last name.
APA and MLA both use a hanging indent, meaning the first line of each entry is flush left and every subsequent line is indented half an inch. Double-space all entries. Do not add extra space between entries in APA. These formatting details are easy to set up in any word processor using the paragraph settings for your reference page.
When you have multiple works by the same author, APA sorts them by year, earliest first. When the same author published two works in the same year, add a lowercase letter after the year (2020a, 2020b) and use those same labels in your in-text citations so the reader knows which source you mean.
Quick Steps to Write Any Citation
- Identify your required style. Check your assignment, syllabus, or publisher guidelines before you start.
- Collect the source details. Author, date, title, publisher or journal, volume/issue/pages, URL or DOI.
- Format the full reference entry. Arrange the details in the order your style requires, with the correct punctuation and italicization.
- Add the in-text citation. Place a shortened reference (usually author and year or author and page number) wherever you use information from that source.
- Cross-check both lists. Every in-text citation should appear in your reference list, and vice versa.
Citation generators built into tools like Google Docs, Microsoft Word, and free websites like Zotero or Scribbr can automate much of this process. They are useful starting points, but always review what they produce. Automated tools frequently get capitalization, italics, and punctuation wrong, especially for unusual source types. Knowing the rules yourself lets you catch those errors before your instructor does.