Paper citation: how to cite sources in your paper

A citation in a paper has two parts. The first is a short note in the text, placed right after the idea or quotation it supports. The second is a full entry in a list at the end of the paper. The note tells the reader which source you mean, and the entry tells them how to find it.

This guide covers both parts in APA 7 and MLA 9. It starts with a routine you can follow while you write, then gives the rule for every case you are likely to meet: one author, many authors, no author, a source quoted inside another source, and a source with no page numbers. It ends with a worked example and a table you can use as a quick reference.

The two parts of every citation

Each in-text citation has to match one entry in the list at the end. A source cited in the text and missing from the list is an error in both styles. So is a source in the list that the text never cites.

Your instructor decides which style to use. If you are not sure, the APA 7 vs MLA 9 comparison explains how to find out and shows the same article cited both ways.

A routine to follow while you write

Most citation mistakes come from trying to rebuild the details at the end. Doing a little at each step is faster.

1. Record the details when you first read a source. Write down the authors, the year, the title, the journal or publisher, the volume, issue and page numbers, and the DOI or web address. Take the page number of every passage you might quote or use. Going back for page numbers later is the slowest part of citing.
2. Mark each idea as a quotation or a paraphrase as you write it. A quotation uses the source’s exact words in quotation marks. A paraphrase restates the idea in your own words. Both need a citation. Putting someone else’s words in your paper without quotation marks is plagiarism even when you cite them.
3. Add the in-text citation in the same sentence. Do not leave a note to add it later. A citation that is not written at the moment you write the sentence is the one that gets forgotten.
4. Add the entry to your list at the same time. Keep the list alphabetical by the first author’s surname.
5. Check the whole list before you submit. Confirm that every in-text citation has an entry, every entry is cited, and every entry matches the source it describes.

In-text citations: the basics

APA: author and year

An APA citation gives the author’s surname and the year of publication. It can be parenthetical, with the details in brackets at the end of the sentence, or narrative, with the author’s name in the sentence itself.

• Parenthetical: Sleep affects exam performance (Okafor & Lindqvist, 2023).
• Narrative: Okafor and Lindqvist (2023) found that sleep affects exam performance.

These two authors are invented for the example.

In a parenthetical citation with two authors, an ampersand joins the names. In a narrative citation, write “and.” The year in the citation is the year only, even if the reference entry gives a month and day.

MLA: author and page

An MLA citation gives the author’s surname and the page number, with no year and no comma between them. The author can be in the parentheses or in your sentence. If the author is in your sentence, only the page goes in the parentheses, and you do not repeat the name in both places.

• With the author in the parentheses: Reading is “just half of literacy” (Baron 194).
• With the author in the sentence: According to Naomi Baron, reading is “just half of literacy” (194).

The page number goes in when you quote or paraphrase a specific part of a source that has pages.

Quotations and paraphrases

Direct quotations

Use quotation marks around the exact words and give the location of the passage.

APA requires the page number, or another location such as a paragraph number, for every direct quotation. APA’s own example is (Ervin et al., 2018, p. 470). When the quotation is 40 words or longer, APA treats it as a block quotation. The block starts on a new line, is indented 0.5 inch from the left margin, and has no quotation marks. The citation goes after the final punctuation of the block, with no period after the closing parenthesis.

MLA also wants the page number: (Baron 194). Use quotation marks for short quotations.

APA’s advice on quoting is worth following in either style. It says paraphrasing is usually better than quoting, because paraphrasing lets you fit the material to your own writing. Quote when the exact wording matters: a definition, something said memorably, or wording you want to respond to directly.

Paraphrases

A paraphrase needs a citation as much as a quotation does. In APA, the page number is not required for a paraphrase, although APA says you may add one when it would help a reader find the passage in a long work such as a book. In MLA, you give the page number of the part you are paraphrasing.

When a paraphrase runs for several sentences in APA, cite the work on first mention. You do not need to repeat the citation as long as it is clear that you are still paraphrasing the same work. Cite it again when you start a new paragraph, and whenever you switch between sources.

The cases that cause trouble

Two authors, three or more authors

In APA, a work with one or two authors names them every time. A work with three or more authors gives the first author plus “et al.” in every citation, including the first: (Martin et al., 2020).

In MLA, two authors are joined by “and”: (Boyd and Nishimura 52). Three or more authors are shortened to the first author plus “et al.”: (Marlowe et al. 52).

An organization as the author

In APA, the organization’s name is the author. If it has a well-known abbreviation, give the full name and the abbreviation the first time, then use the abbreviation: (National Institute of Mental Health [NIMH], 2020) first, and (NIMH, 2020) afterward. A name with no abbreviation is used in full: (Stanford University, 2020).

In MLA, use the organization’s name or a shortened form of it, such as NIH for the National Institutes of Health. Use the same form every time. When an organization is both the author and the publisher, the Works Cited entry begins with the title of the work, and the in-text citation uses that title.

No author

In APA, a work with no author is cited by its title and year. In MLA, it is cited by its title, shortened if it is long, in the parentheses.

No date or not yet published

In APA, a work with no date is cited with “n.d.” in place of the year. A work that has been accepted but not yet published is cited with “in press.”

Two works by the same author

In APA, if two works have the same author or authors and the same year, add a letter to each year, as in 2020a and 2020b, in both the citation and the reference list. In MLA, if you cite two works by one author, add a shortened title to the in-text citation so the reader can tell which work you mean.

A source with no page numbers

In APA, a direct quotation takes a page number or other location information, such as a paragraph number. In MLA, if the source has no page numbers, leave the number out. If the source is a reference-work entry with no page numbers, the citation is the entry’s title alone.

A source you read inside another source

APA says to cite secondary sources sparingly, and MLA says it is best to consult the original and quote from it directly when you can. Either way, finding the original is better.

In APA, name the original source, add “as cited in,” and name the source you actually read: (Rabbitt, 1982, as cited in Lyon et al., 2014). Only Lyon et al. goes in your reference list, because that is the work you read. If the year of the original is unknown, leave it out.

In MLA, the abbreviation is “qtd. in.” The MLA Style Center’s example is (qtd. in Kantor 508), with the name of the person being quoted in your sentence. The Works Cited list has an entry only for the work you actually consulted.

Interviews, emails and other things a reader cannot look up

In APA, a source that readers cannot recover is cited in the text only and does not go in the reference list. This includes personal emails, interviews, unrecorded lectures and similar sources. The citation gives the person’s initials and surname and the most exact date you have: (T. Nguyen, personal communication, February 24, 2020). APA says to use this form only when no recoverable source exists. If a lecture is based on published research, cite the research instead.

Check your instructor’s guidance for this case in MLA, because the right form depends on the kind of source.

Quick reference

Most author names in the table are the examples APA and MLA use in their own guidance, and a few are invented. None of them is a source to look up.

A worked example

Here is a short passage with two citations, followed by the matching entries. The two sources are real articles.

APA 7:

Perception is often described as a form of probabilistic inference (Knill & Pouget, 2004). Deep learning methods have also changed how researchers work with images and speech (LeCun et al., 2015).

References

Knill, D. C., & Pouget, A. (2004). The Bayesian brain: the role of uncertainty in neural coding and computation. Trends in Neurosciences, 27(12), 712–719. https://doi.org/10.1016/j.tins.2004.10.007

LeCun, Y., Bengio, Y., & Hinton, G. (2015). Deep learning. Nature, 521(7553), 436–444. https://doi.org/10.1038/nature14539

MLA 9:

Perception is often described as a form of probabilistic inference (Knill and Pouget). Deep learning methods have also changed how researchers work with images and speech (LeCun et al.).

Works Cited

Knill, David C., and Alexandre Pouget. “The Bayesian Brain: The Role of Uncertainty in Neural Coding and Computation.” Trends in Neurosciences, vol. 27, no. 12, 2004, pp. 712–19, https://doi.org/10.1016/j.tins.2004.10.007.

LeCun, Yann, et al. “Deep Learning.” Nature, vol. 521, no. 7553, 2015, pp. 436–44, https://doi.org/10.1038/nature14539.

The entries come from PaperCitation’s formatter, using each article’s published record. The MLA passage cites the articles as wholes. If you quote or paraphrase a specific part of an article, add its page number.

Notice what stays the same between the two lists. Both are alphabetical by the first author’s surname. Both give the DOI as a full https://doi.org/ link. Both start every entry at the margin and indent any further lines.

Citing a research paper itself

Many people searching for a paper citation want the reference entry for a journal article. The entry follows the pattern in the worked example: authors, year, title, journal, volume, issue, pages and DOI. APA says to include the DOI for every work that has one. The step-by-step guides for a journal article in APA and in MLA explain each element, and how to find a DOI covers the identifier.

Mistakes to look for before you submit

• A source in the text that is missing from the list, or the reverse. Go through the paper once for each direction.
• A quotation without a page number. In APA and MLA, a direct quotation needs its location.
• The wrong style’s habits. A year in an MLA citation, or an ampersand in an MLA entry, shows that APA habits slipped in.
• A copied citation that was never checked. Citations pasted from a database or from another paper’s bibliography can carry errors, such as a wrong year or a missing issue number.
• A source you did not read. If you cite something you only know from another author’s summary, use the secondary-source form above or find the original.
• A reference that cannot be found. This happens with references from AI tools. The post on why AI tools invent citations explains why, and a check takes a few minutes.
• A retracted paper. A paper can be withdrawn after you read it. The post on what a retracted paper means for your reference list covers how to check.

Checking the finished list

PaperCitation’s reference checker looks up each entry in a pasted list, compares the authors, year, title and journal with the published record, and warns you when a paper has been retracted. A reference it cannot match is marked “Couldn’t verify”, which means no record was found, not that the source is invented. The APA and MLA generators build entries from a DOI, an ISBN or a web address, and DOI to citation turns one DOI into an entry in either style.

No tool replaces your instructor’s rules or your own reading of the source. Use the output as a check and a starting point, and compare it with your instructor’s examples.