Socio-technical processes have come to the forefront of recent analysis of the open source software development (OSSD) world. Interest in making these processes explicit is mounting, from industry and the software process community, as well as among those who may become contributors to OSSD organization. This paper serves to close this gap by providing an empirical analysis of the role migration and project career advancement process, and role-sets within, that we have observed through comparative case studies within three large OSSD project organizations: Mozilla.org, Apache.org, and NetBeans.org.