Building on Renee Fox's article 'Training for Uncertainty' and other studies of professional training, this article outlines a conceptual framework for examining several sources of uncertainty and the techniques that trainees learn to control them. It argues that training for control is more the focus of professional education than training for uncertainty, and it suggests that schools of thought in professional work arise around the less certain, unresolved aspects of work. It also examines whether the technical maturity of the field affects the amount of uncertainty that professional students experience or the way in which they are trained to control it. Drawing on the work of Thomas Kuhn, the author introduces the concept of 'paradigm development' and uses studies of medical residencies to show how the nature of uncertainty and the social organization of training may vary by the degree of paradigm development. Finally, the danger of overcontrol is discussed whereby a professional can lose control over the very uncertainties s/he whishes to eliminate.