In terms of prevalence, Obsessive compulsive disorder is the 4th ranked psychiatric disorder. Current treatments include 1st and 2nd wave cognitive behavioural therapies involving exposure and cognitive restructuring. However, 3rd wave therapies such as mindfulness and acceptance and commitment therapy (ACT) are also increasingly recognized as treatments of choice. The current article describes the underlying theory of ACT including relational frame theory, its clinical target: experiential avoidance, its main processes and a tool for the delivery of ACT to patients, the matrix. Rather than aiming to restructure problematic thoughts and evaluations, ACT seeks to train psychological flexibility, the ability to distance from problematic thoughts and accept uncomfortable emotion in the service of engaging personally valued actions. This can help move patient behaviour away from the aversive control of anxiety and obsessions and toward the appetitive control of personal values. The application of ACT to OCD is illustrated by a successful case study.