Literature Review: Twenty-two practice-based evidence studies using the CORE-OM were reviewed and patient outcomes summarised according to mental health provider. Studies using the CORE-OM could be categorised according to four main areas of evaluation, including global service effects, intervention effects, and contextual factor effects. Indications of factors influencing outcomes were considered. Treatment outcomes across mental health services averaged an uncontrolled effect size of 1.23 and RCSI rate of 41.5%. Evidence suggested a range of mental health providers were effective in reducing psychological distress and highlighted understanding both therapeutic change and service effectiveness requires a multifaceted approach. Further research is indicated to develop evidence concerning services beyond primary care and the synergistic effects of multiple factors on outcomes. Empirical report: Secondary analyses of a large practice-based dataset was undertaken from which to determine and compare service profiles, predictors of therapeutic outcome, therapist effects among voluntary sector organisations (VSOs) and national health service (NHS) mental health providers. The sample comprised a total of 10,142 patients and 133 therapists. VSOs and NHS providers were primarily differentiated by their therapeutic orientations, treatment durations, and therapist caseload sizes. Outcomes between sectors were broadly comparable, with recovery rates of 58% and 61% for VSO and NHS providers respectively. VSOs had therapist effects of 4.5%, considerably smaller than therapist effects among the NHS sector (12.7%). Common and specific predictors of outcomes between sectors were identified and explored, with implications for clinical practice and future research discussed.