The pluridisciplinary social science research project « Manufacturing Migrations and Knowledge-related : Mobilities, Productive spaces ans Generations » (sociology, geography, demography, socio-psychology and anthropology) analyses the mechanisms of production of migratory knowledge, as they are the results of the mobilities and the activities of transmigrant and trans-border populations in two areas of the world (North and Central America, Maghreb-Machrek). It aims at studying the international migration social dynamics, according to its space, economic and time dimensions. It leads then to question knowledge society understatements which are commonly used by international organisms discourses. If migrations are easily related to the first two dimensions, partly because of the transnationalization of spaces and economic forces, the time-related dimension of migrations is not so obvious. After decades of repeated migratory circulations in those two areas of the world, we cannot miss the first elements that give this reality a consequent time depth, from all over the migratory generation chain.