Mental health practitioners use behavioral assessment methods in their treatment of clients to target the behavior that is desired, select appropriate treatment strategies, and evaluate treatment outcome. This science-based textbook describes the evidence-based principles and underlying theories of behavioral assessment; demonstrates behavioral assessment methods including behavior observation, interviewing, and client self-report assessments; and provides applications of behavioral assessment. Extensive case study illustrations, sidebar callouts, and other pedagogical tools make this a perfect textbook for courses in psychological assessment, particularly those focusing on behavioral assessment methods.