American Psychological Association | 1,154,055 followers on LinkedIn. Advancing psychology to benefit society and improve lives | The American Psychological Association, in Washington, D.C., is the largest scientific and professional organization representing psychology in the United States and is the world's largest association of psychologists. APA's membership includes more than 157,000 researchers, educators, clinicians, consultants and students. Through its divisions in 54 subfields of psychology and affiliations with 60 state, territorial and Canadian provincial associations, APA works to advance psychology as a science, as a profession and as a means of promoting human welfare.