Cognitive behavior therapy (CBT) represents a family of psychotherapies. Its origins can be traced to the 1960s theories of psychopathology of Aaron T. Beck, who developed cognitive therapy (later referred to as cognitive behavior therapy), as well as Albert Ellis, who developed rational emotive therapy (later referred to as rational emotive behavior therapy), both of which incorporate principles and techniques from behavior therapy (Dobson & Kazantzis, in press;Ellis & Harper, 1961). In the context of psychoanalytic and humanistic models of the time, the CBTs represented a short-term model of therapy; for example, Beck's therapy was initially formulated to treat depression with 20 or fewer sessions, usually with the first eight sessions scheduled biweekly for the purposes of behavioral activation (i.e., treatment aimed at promoting clients' meaningful engagement with the environment). With the inclusion of specific techniques, a focus on session structure, and a core emphasis on between-session therapeutic tasks, referred to as homework, CBT aims to facilitate cognitive, emotional, behavioral, and interpersonal change processes (A. T. Beck et al., 1979). Beck and colleagues adopted a clinical trial methodology to establish the efficacy of their approach in comparison to