With the introduction of Tomorrow's Doctors in 1993, medical education began the transition from a time- and process-based system to a competency-based training framework. Implementing competency-based training in postgraduate medical education poses many challenges but ultimately requires a demonstration that the learner is truly competent to progress in training or to the next phase of a professional career. Making this transition requires change at virtually all levels of postgraduate training. Key components of this change include the development of valid and reliable assessment tools such as work-based assessment using direct observation, frequent formative feedback, and learner self-directed assessment; active involvement of the learner in the educational process; and intensive faculty development that addresses curricular design and the assessment of competency.