Effectiveness of Psychosocial Treatment for Inpatients with Psychosis Patients with psychotic disorders frequently require treatment at inpatient hospital settings during periods of acute illness for crisis management and stabilization. Although these patients often receive efficacious pharmacotherapy, there is a recognized lack of empirically-supported psychosocial interventions provided to patients in typical hospital settings. The provision of high quality psychosocial treatment during hospitalization is challenging due to short lengths of stay and a general lack of trained therapist employed on hospital units who can provide these evidence-based therapies. This unmet need for hospital psychosocial treatment represents a crucial missed opportunity to teach patients coping strategies that can speed time to recovery and impact post-discharge risk factors, including psychotic relapse, treatment nonadherence, suicidality, chronic functional impairment, and rehospitalization. Acceptance and Commitment Therapy (ACT) is a newer cognitive-behavioral approach that combines innovative mindfulness-based strategies for helping patients to cope more successfully with psychotic and other symptoms and implement values-consistent behavioral goals. ACT is the only specific therapy to date that has shown initial efficacy in randomized trials for improving acute and post-discharge outcomes in patients with psychosis when implemented in short-term psychiatric hospitals in the U.S. However, adaptations to the original ACT approach are urgently needed to foster widespread implementation in community settings. There is a need to modify the approach using a more feasible group delivery format that can be administered by routine hospital staff. The aim of the current R34 proposal is to adapt the only promising acute-care psychosocial treatment for psychosis to be implementable in an inpatient setting and pilot test its effectiveness. More specifically, we propose to further develop a comprehensive treatment manual for ACT for Inpatients (ACT-IN) by conducting an open trial (n = 20) in hospitalized patients with psychotic disorders. As part of the open trial, w will implement and evaluate treatment fidelity/competence measures and a therapist training program to evaluate the treatment's implementability among hospital staff. To prepare for a future large-scale clinical trial, we also will conduct a randomized controlled pilot study in a sample (n = 60) of patients hospitalized with psychotic disorders by comparing ACT- IN to treatment as usual to estimate relevant treatment parameters at hospital discharge and 4-month follow- up. In preparation for a future large-scale clinical trial, we will assess the feasibility nd acceptability of the intervention to multiple stakeholders, including consumers. We also will collect pilot effectiveness outcomes, including acute psychiatric symptoms, post-hospital functioning, and rehospitalization rates. This pilot study will lay the groundwork for a fully-powered clinical trial evaluating the effectiveness of this novel psychosocial intervention for improving outcomes in high-risk, hospitalized patients with psychosis.