This paper reports on a theoretical and empirical study into curriculum innovation in secondary education in the Netherlands focusing on mathematics, physics, chemistry, and biology. Curriculum specialists, subject specialists, researchers, policy makers, and teachers were interviewed for the study. Results indicate that mathematics had the most successful innovations. However, even for mathematics where many innovations were realized at the formal level, it was concluded that little is known about what actually happens in classes. In general, the following factors underlying success in curriculum innovation were found to hold across academic subjects: strongly held and detailed views on the teaching of the subject, an emphasis on developmental research or formative inquiries, the creation of support for the innovation in the relevant educational communities, the legitimization of the innovation through new examination structures, the positioning of key-persons in key-positions in educational institutions, detailed and tested curriculum materials as examples for innovations, the involvement of educational publishers, the existence of centers for curriculum research and development, the stimulating role of charismatic persons or centers, and constant attention to networking among teachers and curriculum developers. Contains 19 references. (JRH)