The authors report on the implementation process of environmental education (EE) in two Flemish (Belgian) teacher education colleges. One college had a long history of cross-curricular education, whereas the other college did not. Initially the implementation processes in the two institutions stagnated because of personal and organizational obstructions. After inserting EE in the curriculum for preservice teacher education and in the job descriptions of the participating teachers, the implementation goals. The authors took initiatives and made progress toward the institutionalization of EE. Conflicting priority between mandatory and EE-course time was, however, experienced as a major dilemma in providing EE.