Was there, in different periods of Egyptian history, a clearly defined political and cultural western border? How was the western limit of Egyptian territory perceived and experienced by the central power and local populations? Keeping these questions in mind, the proceedings of the international conference held in Cairo on 2-3 December 2017 explore the western margins of Egypt along four lines: 1) definition, conception, representation; 2) occupation, control, administration; 3) economy; 4) populations, networks, religion. They allow us to sketch a portrait of a key region of Egypt from Antiquity to the Middle Ages. Once the phase of territorial fixation of the Egyptian state was completed, the low population density in the Western Delta and the absence of a real threat did not encourage the definition and defense of an actual western border. However, the arrival of new Libyan groups at the gates of Egypt during the Ramesside period was a turning point. The emergence of the Saite Dynasty placed this region in a new dynamic-that of border with the Greek world and pioneer front-which prefigured the development of this territory under the Ptolemies. During the Roman period, Egypt was part of an empire that extended much further west and whose decision-making center was outside the country, which changed the status of the western limit. Still, the nomadic incursions into the Great Oasis at the end of the period show that the question of the frontier remained an issue. This issue continued after the Arab conquest when Egypt became again part of a vast empire.