model (PBL), which has been applied in the faculties of Engineering and Science, Humanities, and Social Science at Aalborg University since 1974.Since its initial implementation, the PBL model has developed in several important ways. Most notably, the PBL model has developed considerably in relation to the specific nature of the given academic disciplines and become an integrated component of these disciplines.The articles collected in this book seek to describe and explore this development, highlighting variations on the PBL as it was originally conceived and the challenges that have ocurred during this journey.