Careers outside organizations are very often mediated by the activities of intermediaries that place workers in projects across firms. This paper analyzes the role of such intermediaries i.e. staffing agencies in high-skill contractors' careers. As opposed to commonly held conceptions of mediated employment as atomistic, arms -length transactions, I present a picture of this type of work as a relatively organized and socially structured system. I argue that staffing firms may end up reproducing some of the artifacts that we generally associate with organizational career systems, even in a context that is in principle very different from an internal labor market. I draw on learning theories of the employment relationship in order to explain the emergence of bureaucratic structures in this context, and complement these with an emphasis on the relational and social aspects in which mediated work takes place. I analyse client records and individual job histories from a sample of 329 creative IT contractors - web designers, programmers, etc - placed in 2,092 projects by a staffing agency over a 4-year period. I complement these data with insights from 43 semi-structured interviews. Using both quantitative and qualitative analyses, I demonstrate the value of long-term employment for both the staffing agency and its contractors, and explore a number of mechanisms through which tenure premiums arise. I discuss the implications of this study for our theories of careers within and across organizations.