Schema therapy is an integrative treatment approach originally developed for personality disorders, drawing on theory from the cognitive-behavioural, psychodynamic, attachment, and Gestalt therapy traditions. The empirical evidence assessing the efficacy of schema therapy is reviewed in this chapter, with particular emphasis on personality disorders. Schema therapy appears to be an effective psychotherapy for borderline personality disorder with emerging evidence for its efficacy in other areas, such as other personality disorders, affective and anxiety disorders, post-traumatic stress disorder, obsessive–compulsive disorder, eating disorders, autism spectrum disorder, and interpersonal issues. Despite the promising evidence base, much of the research is constrained by methodological issues, such as underpowered samples and insufficient comparison groups. The chapter concludes with future research priorities identified by experts, including clarification of core constructs, broader application across diverse populations, and greater emphasis on cost-effectiveness and understanding therapeutic mechanisms.