Good mental health is a vital part of people’s well-being and essential for individuals and societies to thrive. The recognition that successful mental health strategies need to involve a range of sectors beyond health is not new, yet in practice coalition-building often remains limited and not implemented at scale. This Policy Insights highlights the main findings from the report How to Make Societies Thrive? Coordinating Approaches to Promote Well-being and Mental Health that uses the OECD Well-being Framework to review how people’s economic, social, relational, civic and environmental experiences interlink with their mental health, and uses this evidence to identify policies that can jointly improve both mental health and wider well-being outcomes. Selected mental health initiatives across the OECD are also reviewed to illustrate which elements of the policy ecosystem can support collaboration across government and with society more broadly.