This paper examines the concept of professional trust and argues that trust is an essential component of what it means to be a professional. The first part of the paper discusses the nature of trust in general and attempts to establish two main points: that we are all involved in relationships of trust and that all trust involves risk. The second section examines the idea of professional trust and draws on an analysis of knowledge provided by Michael Oakeshott that divides knowledge into two components, information and judgement. The central argument is that the exercise of judgement through the possession of discretionary powers is central to being a professional, but that judgement itself resists reduction to propositional formulation because it is essentially tacit and individual. The paper's focus is fairly narrow and does not examine, for example, the role of trust in teacher-pupil relationships, how trust may be related to learning or the role of trust in the pursuit of collaborative educational research.