University research scientists epitomise knowledge workers who are positioned to avail of the employment conditions associated with 'boundaryless careers'. Yet while employment flexibility has been hailed as a positive feature of knowledge work, relatively little is known about the forms such flexibility may take or its impact. This article considers the factors shaping the employment conditions of 40 research scientists working in five university research centres in Ireland. The findings suggest that, for knowledge workers such as research scientists, contract employment can deny them access to many of the employment conditions and opportunities that govern their long-term success as researchers. © 2011 © 2011 Taylor & Francis.