The UK All-Party Parliamentary Group (APPG) on complex needs and dual diagnosis was established in 2007 in recognition of the fact that people seeking help often have a number of over-lapping needs including problems around access to housing, social care, unemployment services, mental health provision or substance misuse support. This report sets out the findings from a call for evidence on how social action can improve outcomes and develop more responsive services for people with complex needs or a dual diagnosis. Social action is about people coming together to tackle an issue, support others or improve their local area, by sharing their time and expertise through volunteering, peer-led groups and community projects. The report provides examples of how social action can support recovery, self-worth and confidence, boost employment prospects and skills, reduce stigma, better shape services to meet people’s needs, contribute to better health and wellbeing and save money. It also looks at how to overcome some of the challenges and barriers to developing social action focused around complex needs. These include resources, stigma, procedural issues, leadership, commissioning structures and demonstrating benefits.