This paper describes the principles underlying how various knowledge areas blend into transversal formations in two educational contexts employing PBL. Such "transversality" has often been referred to as inter- cross- or trans-disciplinarity. However, these terms are ambiguous, especially in relation to Problem Based Learning. There is a growing need for stronger language to express underlying principles of knowledge formations and the constitution of such. The term transversality suggests that knowledge formations are not based on a relationship between strong independent disciplines, but rather on a number of subject areas that are combined during students' PBL-studies. As such, the curriculum organized knowledge, as well as students' reflections of various types at the level of teaching and learning, constitute certain "modalities" of transversal knowledge formations. Two institutional case studies--Nursing and the Constructing Architect education--have been researched, compared and contrasted in order to demonstrate how institutional practices demonstrate different modalities of transversal knowledge in their PBL-courses. For the purpose of this paper Nursing Education will be abbreviated as NE and Constructing Architect as CAE.