Today, the diaspora appears as a possible asset, for many countries' development. In this vision, reconnection with high skilled expatriate human resources has acquired a particular momentum. However, this focus outside of the national territory suffers from a lack of tools to translate itself into a tangible contact and actual mobilization. Evidence brought from the CIDESAL project, about Latin-american diasporas, reveals the experimental works and reflections attempted in this direction. Migration trends evolution, occurring at the global as well as regional level, points to the reinforcing process of diaspora constitution. It deserves to be followed and sometimes managed, requiring information gathering and the shaping of adequate instruments 1. The chapter looks at both inputs and brings basic principles for a fertile relationship between diasporas and countries. Biodata : Jean-Baptiste Meyer is senior researcher at IRD. He coordinated the international project "CIDESAL", Creation of Knowledge Diasporas Incubators for Latin America-with the purpose of concretely strengthening network links for effective developments.