• Aaron T. Beck

• Abnormal psychology

• Abraham Maslow

• Activity theory

• Albert Bandura

• Albert Ellis

• Alfred Adler

• Alfred Binet

• Alfred Kinsey

• Alice Miller

• Alogia

• Anal retentiveness

• Analytical psychology

• Anhedonia

• Anna Freud

• Anomie

• Applied psychology

• Archetype

• Aristotle

• Arthur Janov

• Asperger's syndrome

• Attitude (psychology)

• Attribution theory

• Attributional bias

• Aushra Augustinavichute

• Autism

• Avolition