How much do we know about the most effective ways for communities to support people with mental health problems? This paper reviews the quality of evidence available on the effectiveness of different community approaches to mental health. It looks at 48 reviews covering 827 primary experimental and non-experimental studies, published between 2004 and 2017, drawn from the UK and comparable high-income countries. The paper looks mainly at the highest-quality evidence, defined as evaluations drawing on randomised control trials (RCTs), meta-analyses or comparative longitudinal data. This is done with an eye on the community business sector, which is backed by Power to Change and where we hope to see new mental health interventions developed. Using guidelines and definitions established by Public Health England, it assesses what we know about mental health support in the community and what we do not.