The PhD is the highest level of academic qualification, and is by its very nature an exercise in the development of critical thinking. This chapter discusses what it means to study for a PhD and the problems that students have with developing skills of criticality. The author discusses his own experiences of supervising over 50 doctoral students and relates this to the relevant literature. The role that the supervisor, research training, the thesis, dissemination and the viva can play in developing critical thinking are discussed. The power of specific techniques including reflection, action research and action learning are also explored. The chapter presents areas worthy of future study and concludes by presenting an agenda which PhD students and their supervisors might follow.