Which source goes in my reference list?

Only the one you read. In APA, MLA and Harvard the original work appears in your sentence or in-text citation, but not in the reference list. Chicago is the partial exception: its footnote gives full details of both works.

Do I include the year of the original source?

In APA, yes, when you know it: (Miller, 1956, as cited in Cowan, 2001). If the year of the original is unknown, leave it out. Harvard also gives both years. MLA gives no years in the text at all.

Is it bad to use secondary citations?

They are acceptable when the original is out of print, unavailable through your library or in a language you do not read. Used routinely, they are a weakness: you are trusting someone else's summary, and summaries drift from what the original said. A reference list built on as cited in shows how little of it was read at first hand.

What is the difference between a secondary source and a secondary citation?

A secondary source, in the research-methods sense, is any work that analyses primary material, such as a review article or a textbook. A secondary citation, which this guide covers, is the narrower act of citing a work you have not read through a work you have.

What if I then find and read the original?

Cite the original directly and drop the as cited in. If the second author's interpretation also shaped your argument, cite both works separately, each for what you took from it.

How to Cite a Secondary Source (“As Cited In”)

You are reading an article and it describes a finding from an older study that would be perfect for your paper. You have not read the older study. Citing it as though you had is a misrepresentation, and if the article you read got it wrong, the error becomes yours. A secondary citation solves this by telling the reader exactly what you did: you read one work, and it told you about another.

First, Try to Find the Original

APA says to use secondary sources sparingly, for instance when the original is out of print or unavailable, and the other styles likewise expect you to read the original where you can. Before using one:

Look up the original in the reference list of the work you read, and search for its title or DOI.
Check your library and ask about interlibrary loan.
Look for an open-access copy or a preprint.

If you find it, read the relevant part and cite it directly. This often pays off, because originals are frequently more cautious or more limited than later summaries suggest. For sources behind a paywall, see how to cite sources you can't fully access.

The Worked Example

George Miller's 1956 paper on the "magical number seven" is a classic of psychology that many students meet at second hand. Suppose you read about it in Nelson Cowan's 2001 article in Behavioral and Brain Sciences, and you could not obtain Miller's paper. Cowan is the source you read. Miller is the original.

Quick Reference by Major Style

APA (7th Edition)

Parenthetical: (Miller, 1956, as cited in Cowan, 2001)
Narrative: Miller (1956, as cited in Cowan, 2001) proposed that ...

Reference list, the work you read only:

Cowan, N. (2001). The magical number 4 in short-term memory: A reconsideration of mental storage capacity. Behavioral and Brain Sciences, 24(1), 87–114. https://doi.org/10.1017/S0140525X01003922

If you don't know the year of the original, omit it: Miller's study (as cited in Cowan, 2001).

MLA (9th Edition)

George Miller summarized evidence that people can remember about seven chunks in short-term memory tasks (qtd. in Cowan 87).

Works cited, the work you read only:

Cowan, Nelson. "The Magical Number 4 in Short-Term Memory: A Reconsideration of Mental Storage Capacity." Behavioral and Brain Sciences, vol. 24, no. 1, 2001, pp. 87-114, https://doi.org/10.1017/S0140525X01003922.

Name the original author in your sentence. "qtd. in" is short for "quoted in". MLA uses it both for direct quotations and, as here, for paraphrases taken through another source.

Chicago (18th Edition)

Chicago's footnote describes both works, original first.

George A. Miller, "The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information," Psychological Review 63, no. 2 (1956): 81, quoted in Nelson Cowan, "The Magical Number 4 in Short-Term Memory: A Reconsideration of Mental Storage Capacity," Behavioral and Brain Sciences 24, no. 1 (2001): 87.

Take the details of the original from the reference list of the work you read. The bibliography normally lists only the work you consulted (Cowan).

Author-date: name the original in the sentence and cite what you read: In Miller's 1956 paper (quoted in Cowan 2001, 87) ...

Harvard (Cite Them Right)

Quotation: (Miller, 1956, quoted in Cowan, 2001, p. 87)
Paraphrase or summary: (Miller, 1956, cited in Cowan, 2001, p. 87)

Reference list, the work you read only:

Cowan, N. (2001) 'The magical number 4 in short-term memory: a reconsideration of mental storage capacity', Behavioral and Brain Sciences, 24(1), pp. 87–114. Available at: https://doi.org/10.1017/S0140525X01003922

Harvard guides based on Cite Them Right use "quoted in" for the original author's exact words and "cited in" for a summary of their ideas. University College Dublin Library's guide shows the second form: (Waltham, 2010, cited in Seeberg, 2013, p. 10).

IEEE

The IEEE Reference Guide has no secondary citation format, and engineering journals expect you to cite what you read. The usual practice is to number and cite the source you consulted and name the original in the sentence:

Miller's estimate of about seven chunks is discussed by Cowan [1], who argues that the real limit is three to five.
[1] N. Cowan, "The magical number 4 in short-term memory: A reconsideration of mental storage capacity," Behav. Brain Sci., vol. 24, no. 1, pp. 87–114, Feb. 2001, doi: 10.1017/S0140525X01003922.

If the original matters to your argument, obtain it and give it its own reference number.

When a Secondary Citation Is Reasonable

The original is out of print, unpublished, lost or held in an archive you cannot visit.
The original is in a language you do not read, and the work you read translates or summarizes it.
You are discussing how a later author used or interpreted the original, so their account is the thing you are citing.
A textbook or lecture summarizes a classic study and your assignment does not call for primary reading. Check with your instructor; many expect the original at university level.

When It Is Not

The original is a click away. A reference list with many "as cited in" entries for easily available journal articles suggests the reading was not done.
You want the quotation because it is striking. A memorable line quoted at second hand is exactly where transcription errors and lost context creep in.
The claim is central to your argument. Build central claims on sources you have read.

Related Situations

A quotation inside a quotation. If you are reproducing a passage that itself contains quotation marks, the punctuation rules are in how to cite a quote within a quote.

A review article summarizing many studies. If you are using the review's own synthesis, cite the review directly with no "as cited in". The secondary format is only for a specific claim or quotation attributed to a specific earlier work.

A source an AI tool told you about. A chatbot's description of a paper is not a source you can cite through. Find the paper, confirm it exists and says what was claimed, and cite it directly. See how to cite sources you found through AI tools.

Common Mistakes

Listing the original (Miller) in the reference list when you did not read it
Citing the original directly, as though you had read it, by copying its reference from another paper
Reversing the order: the original comes first, the work you read comes second
Using "as cited in" in MLA or "qtd. in" in APA
Giving the page number of the original instead of the page in the work you read
Using a secondary citation for a review article's own conclusions

Sources for These Formats

APA Style, "Secondary Sources" (apastyle.apa.org)
MLA Handbook, 9th ed., on indirect sources, and the MLA Style Center, "Where should the original author's name appear when citing indirect sources?" (style.mla.org/citing-indirect-sources)
The Chicago Manual of Style, 18th ed., on citations taken from secondary sources (chicagomanualofstyle.org)
Pears and Shields, Cite Them Right, on secondary referencing; University College Dublin Library, Harvard style guide, "Secondary sources"
IEEE Reference Guide, version 3.28.2025 (no secondary citation format)

Full style rules: APA, MLA, Chicago, Harvard, IEEE.

The best fix for a secondary citation is the original paper. Wonders searches 320M+ scholarly works, so you can look for the original before settling for “as cited in”.