Behavior therapy is a form of psychotherapy used to treat depression, anxiety disorders, phobias, and other forms of psychopathology. Its philosophical roots can be found in the school of behaviorism, which states that psychological matters can be studied scientifically by observing overt behavior, without discussing internal mental states. Without holding inter states as causal, Skinner's radical behaviorism accepted internal states as part of a causal chain of behavior but continued to hold that the only way to improve the internal state was through environmental manipulation.
Possibly the first occurrence of "behavior therapy" was in a 1953 research project by B.F. Skinner, Ogden Lindsley, and Harry C. Solomon. Other early pioneers in behavior therapy include Joseph Wolpe and Hans Eysenck.
In general, behavior therapy is seen as having three distinct points of origin: South Africa (Wolpe's group), The United States (Skinner), and the United Kingdom (Rachman and Eysenck).Each had its own distinct approach to viewing behavior problems. Eysenck in particular viewed behavior problems as an interplay between personality characteristics, environment, and behavior. Skinner's group in the United States took more of an operant conditioning focus. The operant focus created a functional approach to assessment and interventions focused on contingency management such as the token economy and behavioral activation. Skinner's student Ogden Lindsley is credited with forming a movement called precision teaching, which developed a particular type of graphing program called the standard celeration chart to monitor the progress of clients. Skinner became interested in the individualizing of programs for improved learning in those with or without disabilities and worked with Fred S. Keller to develop programmed instruction. Programmed instruction had some clinical success in aphasia rehabilitation  Gerald Patterson used program instruction to develop his parenting text for children with conduct problems (see ). With age, respondent conditioning appears to slow but operant conditioning remains relatively stable
While many behavior therapists remain stauchly committed to the basic operant and respondent paradigm, in the second half of the 20th century, many therapists coupled behavior therapy with the cognitive therapy of Aaron Beck and Albert Ellis, to form cognitive behavioral therapy. In some areas the cognitive component had an additive effect (for example, sex offender treatment) but in other areas it did not enhance the treatment, which led to the pursuit of Third Generation Behavior Therapies. Third generation behavior therapy uses basic principles of operant and respondent psychology but couples them with functional analysis and a case conceptualization of verbal behavior more inline with view of the behavior analysts.
Behavior therapy is based upon the principles of classical conditioning developed by Ivan Pavlov and operant conditioning developed by B.F. Skinner. There has been up to now a good deal of confusion about how exactly these two conditionings differ and whether the various techniques of Behaviour Therapy have any common scientific base. One answer has come in the form of an online paper called Reinforcing Behaviour Therapy which more and more psychologists are now studying and appreciating.
Contingency management programs are a direct product of research from operant conditioning. These programs have been highly successful. Even with adult who suffer from schizophrenia these programs produce results 
Social skills training teaches clients skills to access reinforcers and lessen life punishment. Operant conditioning procedures in meta-analysis had the largest effect size for training social skills, followed by modeling, coaching, and social cognitive techniques in that order  Social skills training has some empirical support particularly for schizophrenia  However, with schizoprehania behavioral programs in general have lost favor
Applied to Problem Behavior
Behavior therapy based its core interventions on functional analysis. Just a few of the many problems that behavior therapy has created functional analysis for include intimacy in couples relationships , forgiveness in couples, chronic pain, stress related behavior problems of being an adult child of an alcoholic , anorexia,chronic distress , substance abuse , depression , anxiety  and obesity 
Functional analysis has even been applied to problems that therapists commonly encounter like client resistance  Applications to these problems have left cliinicans with considerable tools for enhancing therapeutic effectiveness.
Many have argued that Behavior Therapy is at least as effective as drug treatment for depression, ADHD, and OCD Considerable policy implications have been inspired by behavioral views of various forms of psychopathology.
Rise of a third generation of Behavior Therapy
Of particular interest, in behavior therapy today are the areas often referred to as Third Generation Behavior Therapy. This movement has been called clinical behavior analysis because it represents a movement away from cognitivism back toward radical behaviorism and other forms of behaviorism in particular functional analysis and behavioral models of Verbal behavior. This area includes Acceptance and Commitment Therapy (ACT), Behavioral activation (BA), Kohlenberg & Tsai's Functional Analytic Psychotherapy, Integrative behavioral couples therapy and dialectical behavior therapy. These approaches are squarely within the applied behavior analysis tradition of behavior therapy.
Functional Analytic Psychotherapy is based on a functional analysis of the therapeutic relationship.  It places a greater emphasis on the therapeutic context and returns to the use of in session reinforcement . In general, 40 years of research supports the idea that in session reinforcement of behavior can lead to behavior change 
Behavioral activation emerged from a component analysis of cognitive behavior therapy. This research found no additive effect for the cognitive component . Behavioral activation is based on a matching model of reinforcement. A recent review of the research, supports the notion that the use of behavioral activation is clinically important for the treatment of depression 
Integrative behavioral couples therapy developed from dissatisfaction with traditional behavioral couples therapy. Integrative behavioral couples therapy looks at Skinner (1966)  the difference between contingency shaped and rule governed behavior. It couples this analysis with a thorough functional assessment of the couples relationship. Recent efforts have used radical behavioral concepts to interpret a number of clinical phenomena including forgiveness 
Many organizations exist for behavior therapist around the world. In the United States, the American Psychological Association's Division 25 is the division for behavior analysis. The Association for Contextual Behavior Therapy is another. ACBS is home to many with specific interest in third generation behavior therapy. The Association for Cognitive and Behavior Therapy (Formerly the Association for the Advancement of Behavior Therapy] is for those with a more cognitive orientation. Internationally, most behavior therapists find a core intellectual home in the International Association of Behavior Analysis (ABA:I)  proponents of behavior therapy as tangible evedence
- Systematic desensitization
- Exposure and response prevention
- Behavior modification
- Operant conditioning
- Covert conditioning
- Observational learning
- Contingency management
- Matching law
- Habit reversal training
- Cognitive therapy
- Cognitive behavioural therapy
- Applied Behavior Analysis
- Behavior Modification
- Professional practice of behavior analysis
- Functional Analytic Psychotherapy
- Acceptance and Commitment Therapy
- Dialectical Behavior Therapy
- Behavioral activation
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