The reasons to introduce formats of active learning in engineering (ALE) such as project work, problem-based learning, use of cases, etc. are mostly based on practical experience, and sometimes from applied research on teaching and learning. Such research shows that students learn more and different abilities than in traditional formats of teaching. These abilities are often required by the employers of the alumni and are therefore included in the curricula to educate competent practitioners. A major problem is, however, that a coherent theoretical background explaining the mechanisms underlying ALE is all but lacking. Therefore, it is not clear what the developmental objectives of ALE are. A theoretical basis embedded in learning psychology is needed. A promising concept to fill this gap seems to be the construct of metacognition [Vos 2001, "Metacognition in Higher Education," PhD thesis (Enschede: Twente University Press)] as distinct from cognition. Cognition is concerned with "what" someone knows, metacognition with what people know "about" their knowledge [Flavell 1979, "American Psychologist," 34, 906-911, Metcalfe and Shimamura (eds) 1994, "On Knowing what we Know: Review of Metacognition" (Cambridge, MA: MIT Press)]. Our proposal is that ALE is focused on developing metacognition above or more than cognition. This foundation is important because education for cognitive objectives differs from that for metacognitive ones. Also, metacognitive objectives are more difficult to obtain. The use of founding ALE in the development of metacognition is that knowledge about metacognition serves to formulate clear goals of ALE. From knowledge about metacognitive development, hints can also be derived to raise the effectiveness of ALE. (Contains 1 table.)