Although migration and development are high on the international political agenda today, there is a shortage of data on diasporas in the host countries as well as a lack of information on their transnational practices and impact on the development of their homelands. Among the different types of diasporas, scientific diasporas play a key role as agents of development. This paper will examine the transnational practices of scientific diasporas from developing countries living in Switzerland, which have been set up to reinforce science, technology and development in the home countries. Based on field work carried out in 2007, tracing highly skilled Colombians, Indians and South Africans in Switzerland, this paper will explore the living conditions, working situations and other characteristics of migrants’ daily lives, paying attention to the transnational initiatives and the so-called “giving back” practices that they have towards their homelands. The paper will follow a cross-national comparative approach. While showing the overwhelming pool of value of their practices and initiatives, the paper will provide evidence of the favourable conditions and the obstacles, both in host and home countries, which enable or hinder their transnational initiatives. The paper will validate some hypotheses on the subject of transnationalism, specifically with regard to integration, stability, the loyalties and nostalgia of migrants and their sense of community. Finally, the paper will identify good practices and provide policy recommendations to deepen and enhance the trasnational initiatives of diasporas in a way that will allow them to have a positive sustainable impact in developing countries.