This chapter outlines the philosophical and theoretical underpinnings of Rational Emotive Behavior Therapy (REBT) and places it in a historical context with other models within the cognitive behavioral tradition. The distinctive features of REBT as a model for understanding human psychological function and dysfunction will be outlined and Albert Ellis’s ABC model will be described in detail. In defining the central tenets of REBT theory, the chapter will describe the primary role that rational and irrational beliefs, formed in response to real or perceived stimuli, play in predicting emotional, cognitive, behavioral, and physiological consequences. The chapter will describe how the ABC model can assist sport and exercise psychologists and others working in the field of performance management in the development of assessment, formulation, and intervention strategies.