Over the last ten years, PBL has become an abbreviation for both Problem-Based and Project-Based Learning as it was known from the reform universities that established these pedagogic approaches. There are many reasons for unifying problem-based and project-based learning at a level of learning principles. Especially when implementing PBL in various education systems it calls for a flexible and more abstract definition in order to allow adjustment to the subject area, institutional culture and national educationalframework. But along with the more abstract and unified notion of PBL, there is a growing diversity in the implementation of PBL curricula and therefore an increased need for conceptualisation of diverse practices. This article will present the unifying learning principles along with taxonomies and models for framing the diversity of PBL.