Purpose -This article's aim is to describe the history, purpose, challenges, strategies, and progress of California's Mental Health Oversight and Accountability Commission (MHSOAC), created by California's pioneering Proposition 63 (Mental Health Services Act). California voters passed this initiative in 2004 to expand and transform public mental health services.Design/methodology/approach -This case study is based on observations of the author, who has worked with the Commission since its inception, and the study is adapted from a 2009 article by one of the original Commissioners who served from 2005-2008. The article focuses on challenges and opportunities for oversight in an environment of stakeholders' high and diverse expectations, limited direct state authority, and significant and broad budget challenges.Findings -The Commission prioritizes evaluation as its principal strategy with a primary goal of using evaluation results for quality improvement. Implementing this strategy, with limited county reporting requirements, inadequate data systems, and insufficient funds designated for evaluation, is a continuing challenge. Other key challenges -and opportunities -include passionate stakeholders with high and divergent expectations, a de-centralized public mental health, and a statewide fiscal and budget crisis.Research limitations/implications -The paper relies on the observations of two key participants: a former Commissioner and the Commission's staff psychologist. Participant observation brings opportunities for bias as well as insight. Diverse stakeholders undoubtedly would provide different perspectives on the progress of Proposition 63 and on the MHSOAC.Practical implications -The Commission developed a logic model that defines strategies for oversight and accountability and links these strategies to Proposition 63's intended outcomes for California's public mental health services system and clients.Social implications -The success of California's Proposition 63 in transforming mental health delivery from a ''fail first'' crisis system to a ''help first'' proactive system has implications for integrated healthcare delivery that includes mental health.Originality/value -The California emphasis on recovery, resilience, and wellness for diverse people with and at risk of serious mental illness is consistent with national and world-wide recommendations and initiatives and is one of the largest efforts to transform a mental health system to reflect these values.