Acceptance and commitment therapy (ACT, typically pronounced as the word "act") is a form of psychotherapy and a branch of clinical behavior analysis. It is an empirically based psychological intervention that uses acceptance and mindfulness strategies mixed in different ways with commitment and behavior-change strategies, to increase psychological flexibility. The approach was originally called comprehensive distancing. Steven C. Hayes developed acceptance and commitment therapy in 1982 in order to create a mixed approach which integrates both covert conditioning and behavior therapy. There are a variety of protocols for ACT, depending on the target behavior or setting. For example, in behavioral health areas a brief version of ACT is called focused acceptance and commitment therapy (FACT).

The objective of ACT is not elimination of difficult feelings; rather, it is to be present with what life brings and to "move toward valued behavior".: 240 Acceptance and commitment therapy invites people to open up to unpleasant feelings, and learn not to overreact to them, and not avoid situations where they are invoked. Its therapeutic effect aims to be a positive spiral where feeling better (not in the sense of having "better" feelings, but in the sense of being better at feeling) leads to a better understanding of the truth. In ACT, 'truth' is measured through the concept of 'workability', or what works to take another step toward what matters (e.g. values, meaning).