This ODI Briefing Paper focuses on why and how CSOs can engage more effectively in policy processes in international development. Section 1 sets the scene and highlights the opportunities and challenges facing CSOs policy work. Section 2 focuses on why evidence matters for CSOs’ work in international development. Section 3 provides a framework that matches the engagement mechanisms and evidence needs to the critical stages of policy processes. Section 4 summarises strategic and practical advice on how CSOs can ensure their policy engagement is more effective, influential and sustained