To cite a multi-volume set of books in APA style, use the following format for the references page:
Bowlby, J. (1976-1983). Attachment and loss (Vols. 1-3). New York, NY: Basic Books.
Year published - Check the year published for each volume. If they were published in multiple years, list them as a range where the year typically goes (e.g. 1976-1983).
In the in-text citation, you would cite normally with (Last name, Year) and page number if using quotes. The year would be for the specific volume of the book you are using, since they are all different.
