In 1990, Miller wrote that no tools were available for assessment of what a learner does when functioning independently at the clinical workplace (Miller 1990 ). Since then portfolios have filled this gap and found their way into medical education, not only as tools for assessment of performance in the workplace, but also as tools to stimulate learning from experience. We give an overview of the content and structure of various types of portfolios, describe the potential of electronic portfolios, present techniques and strategies for using portfolios as tools for stimulating learning and for assessment, and discuss factors that influence the success of the introduction. We conclude that portfolios have a lot of potential but that their introduction also often leads to disappointment, because they require a new perspective on education from mentors and learners and a significant investment of time and energy.