The importance of knowledge of curriculum to the success of mainstreaming is explored in this article. The concepts of explicit, hidden, and absent curricula are discussed relative to curricular adaptations that may be necessary to educate handicapped students effectively in the regular classroom. Various issues pertaining to the handicapped and their potential effects upon curriculum implementation are also explored. In addition, a "Curriculum Adaptation Guide" is presented to assist educators in selecting and adapting the most appropriate curricular elements when such adaptations appear necessary. This article emphasizes the concept that special educators should ensure that they are fully knowledgeable about the curriculum in mainstreamed classrooms in order to provide effective assistance to handicapped students and their regular class teachers. Several important curricular topics pertaining to the training of special educators are also presented.