Decentralization reforms have been promoted for four decades as a route to more responsive, efficient, and accountable government. Yet a substantial and growing body of research finds that transferring fiscal, administrative, and political authority to subnational governments frequently outpaces the parallel transfer of oversight capacity, creating gaps that local elites and officials can exploit. This article presents a systematic literature review of the relationship between decentralization, local government oversight gaps, and corruption risk. Drawing on peer- reviewed journal articles, working papers, and institutional reports published between 1998 and 2026, the review synthesizes evidence across three broad strands: (a) cross-country econometric studies of fiscal and political decentralization and corruption; (b) institutional and case-based studies of internal control, audit, and horizontal accountability mechanisms at the subnational level; and (c) political economy studies of elite capture, electoral accountability, and community monitoring. The review finds that the decentralization-corruption relationship is neither uniformly positive nor negative but is conditioned by the design of accountability institutions, the sequencing of reforms, the strength of civil society and media oversight, and the degree of fiscal versus political decentralization pursued. Local oversight gaps understaffed audit units, weak internal controls, limited access to information, and thin electoral competition emerge repeatedly as the proximate mechanism through which decentralization elevates corruption risk. The review concludes by identifying methodological and thematic gaps in the literature and by outlining an agenda for future research and policy design.