This thesis summarises the findings, outcomes, significance and impact of fifty-two papers published in international peer-reviewed journals on the assessment and training of procedural skills in surgery and endovascular disciplines such as interventional cardiology. These studies have identified and quantified human-factor challenges to surgeons and physicians for the practice of image-guided interventional procedures. These difficulties include psychomotor co-ordination of instruments that fulcrum on the body wall thus creating the appearance of counter-intuitive movement at the working end of the instrument. Another difficulty is caused by the degradation of image quality (in comparison to direct viewing) that surgeons and interventionists have to perform the procedure with. These challenges are difficult to overcome and it is inappropriate for these basic skills processes to be learned whilst operating on patients in vivo. A more effective strategy is to train on simulations until a quantitatively defined level of proficiency is achieved. This necessitates the development and the validation of quantification processes. The studies reported here describe the development, the implementation and the evolution of this process in minimally invasive surgery and interventional cardiology and the role that I played in this area. The outcome of this validation process has been the adoption of this approach by major professional medical groupings such as the American College of Surgeons and the American College of Cardiology. It has also been advocated by governmental regulatory organizations such as the Federal Drug Administration (FD A) for the roll-out of cross-disciple interventional procedures such as carotid artery stenting. There is also data to indicate that metric-based assessment has an important function to play in the selection of the next generation of surgeons. Although this approach to medical education and training may be conceptually and intellectually appealing, it represents a paradigm shift from how doctors are currently educated and trained.