Cognitive theory posits that how one interprets an event determines how one feels about it and what one will try to do to cope with it. It further suggests that inaccurate beliefs and maladaptive information processing lie at the core of most disorders. Cognitive therapy seeks to reduce distress and relieve dysfunction by teaching patients to examine the accuracy of their beliefs and to use their own behaviors to test their validity. The history of cognitive therapy is in essence a tale of two cities and one institute. Aaron Beck, the progenitor of the approach, did his original work in Philadelphia focused largely on depression before he expanded to other disorders. He spent time subsequently at Oxford University at the invitation of department chair Michael Gelder, whose young protégés David Clark and Paul Salkovskis refined the cognitive model for the anxiety disorders and supercharged their treatment. Anke Ehlers, who extended the model to posttraumatic stress, joined them in the 1990s before all three decamped for the Institute of Psychiatry in London, only to return a decade later. Jack Rachman at the Institute was an early mentor who commissioned conceptual treatises from all three. Chris Fairburn, who stayed at Oxford, developed a cognitive behavioral treatment for the eating disorders that focuses on changing beliefs, and Daniel Freeman from the Institute joined in 2011 with an emphasis on schizophrenia. Cognitive therapy has had a major impact on treatment in the United States but even more so in the United Kingdom, where it reigns supreme. Cognitive therapy encourages patients to use their own behaviors to test their beliefs but keeps its focus squarely on those beliefs as the key mechanism to be changed. It is one of the most efficacious and enduring treatments for the various psychiatric disorders.