In this paper, the notion of transnational mobility is being questioned in the light of two research projects. The first observes the movements of workers from the hospitality sector in Andorra, and the second deals with Portuguese posted workers in French construction. Comparing these studies enabled us to identify specific traits of transnational mobilities, in contrast to more traditional migrations, especially with respect to time. The resources mobilized by the workers, along with the time and space boundaries of their activities, lead us to question the relationships between networks and migrations. Our principal argument is that social networks are concomitant with mobility, rather than a prerequisite, and are focused on professional activities. This concept takes some distance from a perspective in which networks are bound to communities, places of origin and families. It questions the “already well-established” network, associated with individuals’ practices and trajectories.