In this article, we describe the results of a study of chemistry high school teachers' beliefs (N = 7) of the chemistry curriculum and their roles, their beliefs on the teacher as developer of materials, and their beliefs about professional development. Teachers' beliefs influence the implementation of a curriculum. We view the use of a new curriculum as a learning process, which should start at teachers' prior knowledge and beliefs. The results reveal that it is possible to develop a new curriculum in which teachers' beliefs are taken as a starting point. Promising approaches to prepare teachers for a new curriculum is to let them (co)develop and use curriculum materials: It creates ownership, and strengthens and develops teachers' pedagogical content knowledge (PCK).