Abstract Behavior therapy is a type of psychotherapy that focuses on changing problematic behaviors through the use of techniques based on learning principles. It includes a wide range of strategies, including relaxation‐based techniques, operant conditioning–based strategies, and exposure‐based strategies, among many others. Behavioral techniques are often combined with other treatment strategies, such as with cognitive therapy techniques, in order to most effectively treat psychological difficulties. A thorough behavioral assessment is an important first step before implementing behavioral strategies, and traditional behavioral therapists often conduct a functional analysis of the problem behavior in order to gain a comprehensive understanding of it. This entry discusses the general principles of behavior therapy, provides a brief historical overview, and describes a variety of approaches, including functional analysis, operant conditioning–based strategies, behavioral activation, applied relaxation, and social skills training.