Below you will find guidance and examples of how to reference several volumes of a multivolume work, and how to reference one volume of a multivolume work.
Harris et al. (2012) state that...
...(Harris et al., 2012).
Fiske et al. (2010) believe that...
...(Fiske et al., 2010).
Travis and White (2018) however argue that...
...(Travis & White, 2018).
Several volumes of a multivolume work:
Last name, Initial(s)., Last name, Initial(s). (Ed.). (Year). Title (volume numbers). Publisher. DOI
Harris, K. R., Graham, S., & Urdan T. (Eds.). (2012). APA educational psychology handbook (Vols. 1–3). American Psychological Association.
One volume of a multivolume work:
Fiske, S.T., Gilbert, D.T., & Lindzey, G. (2010). Handbook of social psychology (5th ed., Vol. 1). John Wiley & Sons, https://doi.org/10.1002/9780470561119
If the volume does not have its own title, as in the example above, include the volume number in brackets without italics.
Travis, C.B., & White, J.W. (Eds.). (2018). APA handbook of the psychology of women: Vol. 1. History, theory, and battlegrounds. American Psychological Association. https://doi.org/10.1037/0000059-000
If the volume has its own title, as in the example above, include the volume number and title after the main title in italics.