The purpose of this study is to identify, describe, and analyze historical trends in the professionalization of the field of comparative and international education, as indicated by the founding, expansion, and evolution of the professional associations and graduate programs serving the field. Using historical and university data as well as unique membership data from the Comparative and International Education Society, the authors find that (1) professional associations and university programs in comparative and international education contribute to and secure control over expert knowledge, training and credentials; and (2) the merging of 'comparative' and 'international' education has contributed to the professionalization of the field. In particular, the authors find a simultaneous and complementary process of professionalization and fragmentation occurring within the field of comparative and international education.