PROJECT SUMMARY/ABSTRACT Anorexia nervosa (AN) is a serious illness with extremely high morbidity and mortality rates. Clearly efficacious treatments are lacking for adults with AN, especially during the post-acute stage following higher- level care (e.g., residential, partial-hospital program [PHP]). Most patients achieve symptom stability in intensive treatment, but up to 50% relapse and more experience residual or co-morbid (e.g., affective) symptoms after discharge. Appropriate outpatient treatment is often unavailable or inaccessible in this stage. Despite a rapid growth in the knowledge on the biobehavioral mechanisms promoting AN, this information has rarely been incorporated into treatment. One set of mechanistic targets increasingly acknowledged as relevant to AN are those of the reward system. The reward (a.k.a., positive affect or valence) system has been implicated in maintenance of myriad psychiatric disorders, including common AN co-morbidities (e.g., mood and anxiety disorders). A wealth of evidence, including our pilot data, suggests that individuals with AN show deficit reward sensitivity to experiences generally considered rewarding (e.g., social interactions, eating), similar to those with affective disorders. However, distinct from other psychiatric illnesses, individuals with AN also show elevated reward sensitivity to weight-loss experiences and cues (e.g., exercise, low-calorie foods). Starvation in acute AN appears to exacerbate these processes. However, these same problems affect weight- restored AN, suggesting they represent core illness mechanisms. Although reward anomalies have long been noted in the literature, currently no treatments for AN designate positive affect as a primary intervention target. To remedy this gap, we will test whether a remotely-deployed psychosocial treatment targeting positive affect, Positive Affect Treatment (PAT), can alter reward mechanisms and enhance treatment outcomes in post-acute AN. PAT is a cognitive-behavioral therapy originally designed to treat mood and anxiety disorders and adapted by our team to target reward anomalies in AN (PAT-AN). Our pilot data suggest that PAT-AN, delivered in person or via teletherapy, effectively targets positive affect and reward sensitivity to improve BMI and eating disorder, anxiety, depressive symptoms. We will extend this investigation to the post-acute period of AN, during which we expect to even more effectively engage the reward system, due to the removal of the biological constraints of starvation. Adults with broadly-defined AN (N = 70) leaving residential or PHP will be randomized to 24 weeks of PAT-AN or active control (psychoeducation and behavior therapy) as adjunctive to treatment as usual. Treatment will be delivered via the highly accessible and scalable format of teletherapy. Throughout treatment and follow-up, subjects will complete a novel multimodal battery (e.g., mobile-delivered and neurocognitive measures) assessing measuring r...