This PhD thesis addresses the question of how we define, measure and improve surgical judgment and decision making, and how junior surgeons may be trained in these skills. The introduction to the thesis outlines the importance of surgical decision making, and the rationale for undertaking this research. An overview of relevant cognitive psychology research is presented, and the methodologies used in the experimental chapters of the thesis are described in detail. The introduction concludes with a systematic review of published empirical work on surgical decision making. The first two empirical studies are qualitative in nature, using interviews and simulation. They address how we define surgical decisions and their relationship to the process of care, including how surgeons subjectively view their own decision making, and whether we can we draw inferences from observation of the process in action. Subsequent experimental chapters focus on the measurement of the quality of judgments of risk – a pre-decisional process in which likely outcomes of surgery are evaluated and estimated. Judgment analysis methodology is used to measure surgeons’ performance at estimating surgical risks, with evaluation of whether the method shows construct validity, and whether feedback derived from judgment analysis tasks can be used as a teaching tool. The final empirical section of the thesis develops the theme of training junior surgeons in understanding risk and becoming better decision-makers. The process of developing, piloting, implementing and evaluating of a course module aiming to improve surgical trainees’ approaches to decision making is presented. Finally the discussion reflects on the strengths and weaknesses of the studies, and outlines the implications of the work for clinical practice, training of junior surgeons, and future research.