A "secondary source" is a source cited within another source. Sometimes, this is called an "indirect source" or an "indirect citation".

It is always best to find and cite the original source. But, sometimes it is unavailable. For example, a book may be out of print, in a foreign language, or hard to obtain. If that’s the case, you may find that you need to cite the secondary source instead.

If you need to cite a secondary source, follow these guidelines: 

• In the text, identify the primary source and write “as cited in” the secondary source that you used.
• If the year of publication of the primary source is known, also include it in the in-text citation.
• In the reference list, provide an entry for only the secondary source that you used.

Example:

In-Text Citation:

As Michael Foucault (1969, as cited in Kendrick, 2001) noted, “The archive determines our knowledge and sense of history by what it includes and what it leaves out” (p. 135).

OR

“The archive determines our knowledge and sense of history by what it includes and what it leaves out” (Foucault, 1969, as cited in Kendrick, 2001, p. 135).

Reference list:

Kendrick, J. (2001). What is the criterion? The criterion collection as an archive of film as culture. Journal of Film and Video, 53(2), 124-139.

For more information, see the SAE APA Referencing Guide.