The public sector is the single most important investment instrument for the state, and improving the way it is managed is critical for development outcomes including service delivery, social protection and private sector regulation. Public sector governance reform involves institutional reform – that is, changing the rules and norms that govern public sector activity. How can policymakers and practitioners support institutional reform to improve the performance of the state? What do we know about what has – or hasn’t – worked, and where? This Topic Guide synthesises the evidence, debates and lessons that emerge from the literature.