This dissertation explores the application of spatial organization models to medieval Islamic urbanism. In particular, the systems of urban settlements in Mesopotamia and Persia during the ninth and tenth centuries A.D. are investigated, depending primarily on medieval indigenous sources. The study of Islamic urbanism in general, and medieval Islamic urbanism in particular, remained for a long time obscured by an inadequate single perspective: the "Islamic city" as an individual social entity occupying a fixed geographical area. The conventional approach can be criticized for its restricted focus on Islamic cultural tradition as the only explanatory variable and for its search for an ideal-type construct in the tradition of Western urban-ecological writings of the first half of the twentieth century. The alternative approach put forward in the present thesis examines the city as part of a larger urban network extending over several regions. It is argued that the application of spatial organization models to medieval Islamic urbanism will help to clarify the place and role of cities in both the regional and national structures and will provide a suitable framework for comparing the stages of urban and regional development. Following a historical perspective, the study results indicate the sequence in the evolution of a distinctive form of Islamic urbanism through the operation of several spatial processes. Such processes signify the expansion, assimilation, and integration of urban settlements in former Sasanian lands. Analysis of the road network provides the necessary framework by which interurban contacts are examined on both the national and the regional levels. Hierarchical organization of space and settlement interdependencies are further demonstrated by the analysis of long-distance kharaj (land tax) mobility. This medieval fiscal system is used as a surrogate for human spatial interaction and is supplemented by an evidence for the existence of an urban hierarchy derived from the actual methods and approaches used by the medieval Arab geographers themselves. The findings of the present study demonstrate the evidence for the evolution first of a nationally integrated urban system and second of several regionally organized urban subsystems.