The present thesis is concerned with the study of the grid structure of Arab towns found across North Africa. Studies on this kind of towns have stressed the idea of a single city form based on a threefold hierarchical organisation of space with a specific emphasis on the cul-de-sacs; and the division of the town into a central public core and more private residential quarters. This spatial model has often provided the rationale for the design of new housing layouts. Ground plans of Arab towns, however, often show great variation in the grid structure, ranging from a very regular pattern to a strongly deformed and labyrinthine type, suggesting then that the idea of a single city type is unsatisfying. It also seems to be the case that plans of modern housing layouts based on concepts derived from this model bear little resemblance, when built, to traditional urban forms. On both counts, therefore, the model seems too abstract and too generalized to give a satisfactory account on Arab cities. The study examines these issues in the light of a descriptive theory of urban space and argues that grid structures of Arab towns present typological tendencies and morphological individualities as well as generic properties. More particularly, it suggests that: i- underlying the grid structure of Arab towns, there are generic similarities, in that the urban fabric is highly segregated, and presents a strong regionalization of the integrating spatial structure; ii- there are strong typological differences mainly in the degree of deformation of the urban grid, in that some towns have some degree of regular structure imposed on the plan, while others clearly lack regularity; differences in the overall pattern of the integrating structures; and the degree to which the spatial structure of the quarters links to each other and to the whole fabric to form a connected structure. The study suggests that both the fundamental similarities and the deep differences in the structure of these towns arise from a single dominant factor: the degree to which the grid structure is deformed to produce firstly, a certain type and degree of movement interface between the most permanent users, i.e. the inhabitants, and visitors of the towns; and secondly a certain type and degree of movement interface among the inhabitants of the separate quarters of the town. These conclusions are then used as a basis for reconsidering some recent typical 'traditionalist' design concepts, such as the clustering of dwelling units adopted in the modern layouts. Finally, the study argues that the regulation of the overall grid deformation can itself be used as a basic design concept to re-produce these types of movement interface. For this, the study explores the possibility of using a computer-based generative process of grid patterns, in which spatial properties of the grid of Arab towns have been introduced as an eventual basis for the design of housing layouts.