The APA author-date system is the standard in STEM, psychology, and social sciences. This guide covers every scenario: single and multiple authors, organisations, no author, no date, quotations, secondary sources, and personal communications — all with worked examples.
Every time you use someone else's idea, data, or words in APA, you place a brief citation inside your text. That citation has two core elements: the author's last name and the year of publication. These two pieces point the reader to the full reference in your Reference List.
There are two ways to structure the same citation in your prose:
| Format | When to use | Example |
|---|---|---|
| Parenthetical | The source is evidence for a claim — the author is not the focus of the sentence | Immune evasion is a primary driver of treatment resistance (Chen et al., 2023). |
| Narrative | The author is the subject — you want to credit them as the agent of the finding | Chen et al. (2023) demonstrated that immune evasion drives treatment resistance. |
Both formats are equally correct. Academic writing in STEM tends to use parenthetical more often — findings are the focus, authors are secondary. Use narrative when you want to emphasise who made a finding, compare competing findings, or attribute a specific methodology.
APA 7th edition changed the rules for multiple-author sources compared to 6th edition. The table below applies to both first and subsequent citations — APA 7th no longer uses "et al." only after the first mention:
| Number of authors | In-text format | Example |
|---|---|---|
| 1 author | Author (Year) | (Patel, 2022) |
| 2 authors | Author & Author (Year) | (Müller & Kim, 2021) |
| 3 or more authors | First author et al. (Year) | (Rodriguez et al., 2023) |
APA 7th vs 6th — key change: APA 6th used full author lists for the first citation of a 3–5 author paper (Smith, Jones, & Park, 2020) and shortened to et al. only from the second citation. APA 7th uses et al. from the very first citation for any source with 3 or more authors. If you are using 6th edition, confirm this with your institution before switching.
If two different works both shorten to "Chen et al. (2023)", add enough additional authors to distinguish them:
Note: In narrative citations, use "and" between two authors in running text (Müller and Kim) — not the ampersand (&). The ampersand is only used inside parentheses.
When a government body, company, or organisation is the author, spell out the full name in the first citation. If the organisation has a well-known abbreviation, you may introduce it in brackets and use the abbreviation in subsequent citations.
Our STEM writing specialists review in-text citations and reference lists against APA 7th edition standards.
When a source has no identifiable author, use a shortened version of the title in place of the author. Use the first few significant words to allow readers to locate it in the Reference List.
When a source has no publication date — common with website content, corporate pages, and older institutional documents — use "n.d." (no date) in place of the year.
Page numbers are required in APA when directly quoting. They are recommended but not required when paraphrasing — adding them helps readers locate the specific passage, which is good practice in long sources.
| Source type | Locator to use | Example |
|---|---|---|
| Printed book or journal | p. (one page) / pp. (range) | (Chen et al., 2023, p. 45) |
| Chapter in a book | p. / pp. as above | (Patel, 2022, pp. 112–116) |
| Website / no page numbers | Paragraph number: para. | (WHO, 2023, para. 3) |
| Ebook with locations | "Location" or chapter | (Kim, 2021, Chapter 4) |
| Video | Timestamp | (3Blue1Brown, 2017, 2:34) |
When a claim is supported by more than one source, list them all in the same parentheses, separated by semicolons. Order them alphabetically by the first author's name.
If all sources in a group are by the same first author, order them by year:
If you cite two papers by the same author(s) published in the same year, add letters (a, b, c…) to distinguish them. These letters also appear in the Reference List:
A secondary source is one cited within a source you are reading. Ideally, you should locate and read the original. When the original is unavailable (out of print, inaccessible language, no institutional access), you may cite it as a secondary source.
Format: the original author's name + "as cited in" + the source you actually read.
Limit secondary sources. Using too many secondary citations signals that you have not engaged with the primary literature. Markers and reviewers view them as weak evidence. Reserve them for truly inaccessible sources.
Personal communications include emails, interviews, phone calls, text messages, and conversations. Because they cannot be retrieved by the reader, they are cited in-text only — do NOT add them to the Reference List.
For classical or ancient works (the Bible, ancient Greek texts, early scientific treatises) where the original publication year is far removed from the edition you are using:
For translated works, also cite the original year where known.
| Scenario | Parenthetical | Narrative |
|---|---|---|
| 1 author | (Patel, 2022) | Patel (2022) |
| 2 authors | (Müller & Kim, 2021) | Müller and Kim (2021) |
| 3+ authors | (Rodriguez et al., 2023) | Rodriguez et al. (2023) |
| Organisation (first) | (World Health Organization [WHO], 2023) | World Health Organization (WHO, 2023) |
| Organisation (subsequent) | (WHO, 2023) | WHO (2023) |
| No author — article | ("Antifungal Resistance," 2023) | "Antifungal Resistance" (2023) |
| No author — book/report | (Global Report, 2022) | Global Report (2022) |
| No date | (WHO, n.d.) | WHO (n.d.) |
| Direct quote | (Chen et al., 2023, p. 45) | Chen et al. (2023, p. 45) |
| Same author, same year | (Chen et al., 2023a) | Chen et al. (2023a) |
| Multiple sources | (Almeida, 2021; Chen et al., 2023) | — |
| Secondary source | (Michaelis, as cited in Berg et al., 2022) | Michaelis (as cited in Berg et al., 2022) |
| Personal communication | (B. Liu, personal communication, March 3, 2023) | B. Liu (personal communication, March 3, 2023) |
No — but you need to make clear which ideas are from sources and which are yours. If multiple consecutive sentences continue the same source's argument and the attribution is clear from the previous sentence, a single citation at the end of the paragraph is usually sufficient. However, if a new source's idea begins mid-paragraph, cite it immediately to avoid ambiguity.
APA uses parenthetical in-text citations, not footnotes for references. APA does use footnotes — but only for supplementary information that would disrupt reading flow, not for citations. Do not use footnotes to replace in-text citations in APA.
Use a shortened title and "n.d.": ("Antifungal Resistance," n.d.) or (Global Report, n.d.). This combination is common with some government web pages and institutional documents that lack a named author and a publication date.
Yes. If you create your own figure or table using data from a published source, the figure/table caption must include a note citing the original source. The in-text citation rule still applies — cite the source whenever you present the data, whether in prose or visually.