The last twenty years has seen calls for greater coordination between security and development policy, based on assumptions of the interconnectedness of security and development. Since 9/11 and the War on Terror (WoT), the national security of Western states has been added to this relationship. This research seeks to understand this dimension of development aid contributing to donor national security: as part of mainstream development policy, over an extended period of time and across multiple donors. This is done through content and discourse analyses of donor policy documents complemented with interviews with key informants in donor development agencies and fieldwork interviews in Ethiopia and Kenya. This case study approach: looks at a time period from the late 1990s to 2012 to capture the merging of security and development both pre and post-9/11; looks at the US, the UK and Canada to separate out the differences between donors approaches; looks at both the development and security policy of these donors to capture any influence development has on security in addition to security influencing development; and looks at how these donors have dealt with security in their development programmes in Ethiopia and Kenya. From this it is argued that in the security-development nexus, development aid is expected to manage long-term risks to the national security of donors.