Is it plagiarism if I cite my own previous work?

Depending on the circumstances, it can sometimes be plagiarism to cite your own previous work.

For example, in the context of published works the Publication Manual of the American Psychological Association (APA, 7th edition) defines self-plagiarism as "the act of presenting one's own previously published work as original: it misleads readers and falsely inflates the number of publications on a topic. Like plagiarism, self-plagiarism is unethical." (Section 1.17)

Regarding reusing one's unpublished works, Section 8.3 of that Manual discusses how to avoid self-plagiarism, including but not limited to:

• ensuring compliance with the university's academic integrity policy, honor code, or ethics code. For example, please see also the attached link to the Academic Integrity Policy for Students at this University of Notre Dame Australia, which includes reference to self-plagiarism
• seeking prior permission from the current course instructor before (re)submitting part of a paper that has been written for one class, in order to complete an assignment for another class

A related APA7 document link is also attached.