This chapter discusses planning theory from two perspectives: theories of planning as a process, both how it ought to be done and how it is done, and some ideological issues. It also discusses ideologically based criticisms of planning-both the idea of planning and planning as actually practiced. The chapter addresses four approaches to the process of planning: the rational model, disjointed incrementalism, a middle-range approach and collaborative rationality. The rational model has been prevalent for several decades and might be considered to be the orthodox view. The underlying philosophy behind collaborative rationality is somewhat different than that behind the rational model. Those who favor collaborative rationality tend toward a more horizontal rather than a hierarchical view of the planning process. Collaborative rationality is somewhat different in character, in part because of its different philosophical roots. Booher and Innes, two of its most prominent academic proponents, characterize collaborative rationality's basic requirements as diversity, interdependence, and authentic dialogue.