The social sciences hold the potential to help interpret and address the complex challenges confronting society. The impact agenda actively encourages the social sciences to make and demonstrate a difference; to justify and protect social science funding. Knowledge mobilisation (KM) can be thought of systematically as a process, encompassing the co-production and channelling of knowledge that can enable the social sciences to gain purchase and voice in the policy-making and delivery process, and supports the endeavour to make a difference. This article serves as an editorial introduction to a special issue in two parts: ‘KM: Research Impact’ and ‘KM: Engagement’. It sets out to outline the forces leading to the rise of the impact agenda and the questions it poses for the social sciences. Particular attention is given to the changing policy context that has reshaped the academy. The article then progresses to outline debates on research and impacts and the forms of engagement that are needed to demonstrate and deliver impact beyond the academy. The article examines the ways in which impact is defined, measured and ‘delivered’ within the social sciences. This is followed by a section on the ways in which social science knowledge is mobilised. The penultimate section addresses the co-production of social scientific knowledge and this is followed by a brief conclusion.