Dialectical behavior therapy (DBT) is an evidence-based psychotherapy that began with efforts to treat personality disorders and interpersonal conflicts. Evidence suggests that DBT can be useful in treating mood disorders and suicidal ideation as well as for changing behavioral patterns such as self-harm and substance use. DBT evolved into a process in which the therapist and client work with acceptance and change-oriented strategies and ultimately balance and synthesize them—comparable to the philosophical dialectical process of thesis and antithesis, followed by synthesis.

This approach was developed by Marsha M. Linehan, a psychology researcher at the University of Washington. She defines it as "a synthesis or integration of opposites". DBT was designed to help people increase their emotional and cognitive regulation by learning about the triggers that lead to reactive states and by helping to assess which coping skills to apply in the sequence of events, thoughts, feelings, and behaviors to help avoid undesired reactions. Linehan later disclosed to the public her own struggles and belief that she suffers from borderline personality disorder.

DBT grew out of a series of failed attempts to apply the standard cognitive behavioral therapy (CBT) protocols of the late 1970s to chronically suicidal clients. Research on its effectiveness in treating other conditions has been fruitful. DBT has been used by practitioners to treat people with depression, drug and alcohol problems, post-traumatic stress disorder (PTSD), traumatic brain injuries (TBI), binge-eating disorder, and mood disorders. Research indicates that DBT might help patients with symptoms and behaviors associated with spectrum mood disorders, including self-injury. Work also suggests its effectiveness with sexual-abuse survivors and chemical dependency.

DBT combines standard cognitive-behavioral techniques for emotion regulation and reality-testing with concepts of distress tolerance, acceptance, and mindful awareness largely derived from contemplative meditative practice. DBT is based upon the biosocial theory of mental illness and is the first therapy that has been experimentally demonstrated to be generally effective in treating borderline personality disorder (BPD). The first randomized clinical trial of DBT showed reduced rates of suicidal gestures, psychiatric hospitalizations, and treatment dropouts when compared to usual treatment. A meta-analysis found that DBT reached moderate effects in individuals with BPD. DBT may not be appropriate as a universal intervention, as it was shown to be harmful or have null effects in a study of an adapted DBT skills-training intervention in adolescents in schools, though conclusions of iatrogenic harm are unwarranted as the majority of participants did not significantly engage with the assigned activities with higher engagement predicting more positive outcomes.

DBT is sometimes considered a part of the "third wave" of cognitive-behavioral therapy, as DBT adapts CBT to assist patients in dealing with stress. DBT focuses on treating disorders that are characterised by impulsivity and emotional dysregulation.

DBT strives to have the patient view the therapist as an accepting ally rather than an adversary in the treatment of psychological issues: many treatments at this time left patients feeling "criticized, misunderstood, and invalidated" due to the way these methods "focused on changing cognitions and behaviors." Accordingly, the therapist aims to accept and validate the client's feelings at any given time, while, nonetheless, informing the client that some feelings and behaviors are maladaptive, and showing them better alternatives. In particular, DBT targets self-harm and suicide attempts by identifying the function of that behavior and obtaining that function safely through DBT coping skills. DBT focuses on the client acquiring new skills and changing their behaviors, with the ultimate goal of achieving a "life worth living".

In DBT's biosocial theory of BPD, clients have a biological predisposition for emotional dysregulation, and their social environment validates maladaptive behavior.

DBT skills training alone is being used to address treatment goals in some clinical settings, and the broader goal of emotion regulation that is seen in DBT has allowed it to be used in new settings, for example, supporting parenting. There has been little study into adapting DBT into an online environment, but a review indicates that attendance is improved online, with comparable improvements for clients to the traditional mode.