Journal article: Migration decisions affect those left behind in ways that are for some part taken into account by market forces (e.g., wage effects on labor markets) and for the most part that can be seen as pure externalities. Diasporas are an example of such externality. This article reviews the recent economic literature on diaspora networks and development. It is split into two parts: a first section reviews the effect of diaspora networks on trade, foreign investments, and the diffusion of knowledge across borders. A second section looks at the cultural sway of the diaspora, investigating the role of emigrants in the formation of political attitudes, fertility behavior, and other aspects of culture.