The importance of public and user involvement in the development and delivery of research, policy and practice is now widely recognised. Nonetheless, service providers continue to experience difficulties in meaningfully involving service users and carers in their work in spite of the fact that this is a legal and policy requirement. Researchers, policy makers and providers do not always have the knowledge and skills effectively to involve the public and service users and carers. This case study describes the very significant impact of one piece of research designed to address these challenges in Northern Ireland. This research is presented as an example of impact because it has resulted in significant changes to the policies and practices of the three key organisations funding the research.