At the World Summit in 2005, United Nations member states unanimously endorsed the ‘Responsibility to Protect'. This acknowledged the responsibility of states to protect their populations from genocide and mass atrocities, but also that of the international community, acting "through the United Nations". A strong focus of the statement is on the necessity of prevention, and the appropriate "diplomatic, humanitarian and other peaceful means" the United Nations can employ in its service. But what capacity does the United Nations currently have to help protect populations from genocide, war crimes, crimes against humanity and ethnic cleansing through preventative action? Is it adequate, or are there areas where capacity building is required? This paper will explore the current capacity to meet the ‘responsibility to prevent' within the United Nations system. It will identify areas of strength that might be more explicitly utilised in support of prevention measures, and areas in which there are opportunities for improvement. Finally, it will consider the potential of mainstreaming Responsibility to Protect considerations across the United Nations system.