Increasing research has illustrated the positive effects of the diaspora on the country of origin. The majority of this research, however, has focused on the effects of diaspora remittances and investments. This article examines the effects of the diaspora on knowledge transfer and capacity building in a post‐conflict environment. The article is based on a case study of the International Organization for Migration the Netherlands, Temporary Return of Qualified Nationals to Afghanistan project, in which 59 highly skilled Dutch‐Afghans returned to work with a host institution (public or private) in Afghanistan for three months to transfer knowledge and build capacity. In‐depth interviews were conducted with project participants, host institutions, participants' colleagues, and key informants to gather an understanding of how participants contributed. The article finds that diaspora temporary returnees were most effective in forms of tacit knowledge transfer and that the knowledge transfer process effectively led to capacity building in Afghanistan.