Noting that the process of writing textbooks has seldom been studied, this paper offers a process-product model that relies on a systems analysis of the textbook universe (or megasystem) to provide insight into the textbook writing process. The model presented discloses the interaction of a number of boundaried but interdependent "peer systems," including the family system, the government system, the knowledge production system, the educational delivery system, and the knowledge distribution system. The paper notes that smaller, but nonetheless influential "satellite systems" affect the system as well, such as religious bodies, parent organizations, teachers' organizations, and self-constituted textbook critics. The paper next points out how perplexing perturbations in the family and government systems arose in 1986 and 1987 when parents brought suit against two school boards in Tennessee and Alabama about textbook content. A process-product analysis of the evolution of the textbook from blank page to manuscript page is presented next, followed by a description of the relationship between textbook writing and the knowledge production system (colleges and universities). Discussions of motivations of textbook authors, such as the opportunity for creativity and intellectual challenge, and the mission of textbook writing, are the topics of the final two sections of the paper. A table presenting a taxonomy of the peer and satellite systems in the ecology of education and 60 references conclude the paper. (SKC)