The aim of the Outcome Questionnaire (OQ) system is to provide measures and methods to enhance treatment outcomes for psychological disorders, especially for patients whose progress and eventual positive outcome are in doubt, by providing progress information directly to practitioners. The system consists of several adult and youth measures contained in the software [Page 2405]OQ-Analyst. This entry first describes the measures in the OQ system and then discusses various aspects of the system, including the domains assessed, psychometric properties, assessment, and feedback from clinicians and patients.