Anhedonia, or loss of interest or pleasure in usual activities, is characteristic of depression, some types of anxiety, as well as substance abuse and schizophrenia. Anhedonia is a predictor of poor long‐term outcomes, including suicide, and poor treatment response. Because extant psychological and pharmacological treatments are relatively ineffective for anhedonia, there is an unmet therapeutic need for this high‐risk symptom. Current psychological and drug treatments for anxiety and depression focus largely on reducing excesses in negative affect rather than improving deficits in positive affect. Recent advances in affective neuroscience posit that anhedonia is associated with deficits in the appetitive reward system, specifically the anticipation, consumption, and learning of reward. In this paper, we review the evidence for positive affect as a symptom cluster, and its neural underpinnings, and introduce a novel psychological treatment for anxiety and depression that targets appetitive responding. First, we review anhedonia in relation to positive and negative valence systems and current treatment approaches. Second, we discuss the evidence linking anhedonia to biological, experiential, and behavioral deficits in the reward subsystems. Third, we describe the therapeutic approach for Positive Affect Treatment (PAT), an intervention designed to specifically target deficits in reward sensitivity.