This paper aims to explore the late-nineteenth and early-twentieth-century history of the frontier between modern-day Libya and Egypt through the lens of the Sanusi Islamic Brotherhood (Sanusiyya)—a revivalist, Sufi-inflected religious order that established itself in the middle of the expansive Libyan Desert in the early-1840s. A mere half-century after its founding, the Sanusiyya had become a major power-broker in the amorphous desert territory that comprised the western-most reaches of Egypt and the eastern portion of Ottoman-administered Libya (the province of Benghazi). Historians of the modern Middle East have tended to adopt, unquestioningly, a well-worn narrative of Egypt’s uniquely successful rise among Ottoman provinces in the nineteenth century as a modern centralizing nation-state, without critically examining the question of what state sovereignty looked like in any of its far-off marginal territories, such as the northwest Mediterranean coastline or the Libyan (Western) Desert. My analysis of Sanusi authority along Egypt’s western frontier seeks to provide a necessary revision along these lines. First, I will analyze Sanusi practices of education, justice, and warfare, as well as cross-border economic linkages and regional notions of sacred geography, in order to demonstrate how local conceptions of space, politics, and identity among the (mostly bedouin) population over which the Sanusiyya held sway countered the efforts of the Egyptian authorities in Cairo to construct a cohesive territorial nation-state. Second, I will argue that the Sanusiyya practiced a distinctive border politics that succeeded by capitalizing on the unresolved question of state power at the frontier, given that the nature of the Ottoman-Egyptian relationship – particularly in relation to control over borderlands – was wholly ambiguous. Ultimately, I hope that my study of the Sanussiyya will offer a broader sort of social history of the Egyptian West in the decades leading up to World War I, and point the way towards a new approach to the thorny issues of local politics and identity, as well as Ottoman and Egyptian territorial sovereignty, in the era of the modern centralizing nation-state.