The Arab conquest of Egypt in 642 AD affected the development of Egyptian towns in various ways. The actual military struggle, the subsequent settling of Arab tribes and changes in administration are discussed in chapter 1, with reference to specific sites and using local archaeological sequences. Chapter 2 assesses whether our understanding of the archaeological record of the seventh century is detailed enough to allow the accurate dating of settlement changes. The site of Zawyet al-Sultan in Middle Egypt was apparently abandoned and partly burned around the time of the Arab conquest. Analysis of surface remains at this site confirmed the difficulty of accurately dating this event on the basis of current information. Chapters 3 and 4 analyse the effect of two mechanisms of Arab colonisation on Egyptian towns. First, an investigation of the occupation by soldiers of threatened frontier towns (ribats) is based on the site of Tinnis. Examination of the archaeological remains indicates a significant expansion of Tinnis in the eighth and ninth centuries, which is confirmed by references in the historical sources to building programmes funded by the central government. Second, the practice of murtaba ` aljund, the seasonal exploitation of the town and its hinterland for the grazing of animals by specific tribal groups is examined with reference to Kharibta in the western Delta. Kharibta had apparently declined in size and prosperity by around the eleventh century. Chapter 5 considers the development of the important Pharaonic administrative centre of Edfu in Upper Egypt. Exposed archaeological sequences have clarified the movement of settlement in the town eastwards during the Islamic period. The final chapter proposes two factors that have hitherto not been given sufficient weight. First, the importance of military settlement in promoting settlement change; and second, the flawed nature of our understanding of the urban archaeological record for this important period. The thesis concludes with a suggested paradigm of urban transition, which will allow greater understanding of the changes in settlement in Roman and Islamic Egypt.