["Transactions of the Institute of British Geographers, Volume 51, Issue 2, June 2026. ", "\nShort Abstract\nFocusing on the rapid urbanisation of Sihanoukville, Cambodia, this article analyses the rise of offshore urbanism as a planning model aligned with offshore financial logics. It shows how spaces of exception and financialisation converge to plug urban territories into the grey circuits of global finance, reframing opacity, rent‐seeking and weak regulation as comparative advantages. In doing so, the article sheds light on the underexplored underground dynamics of planetary urbanisation.\n\nABSTRACT\nThis article explores the growing influence of offshore finance on urban and territorial planning in the Global South by analysing the fast urbanisation of Sihanoukville, Cambodia's main port city. Since the early 2020s, a new master plan has been designed to transform the city and its province into a multi‐purpose SEZ, while positioning Sihanoukville as a new offshore financial centre. We argue that this process exemplifies the emergence of what we conceptualise as offshore urbanism: a form of urban and territorial production inspired by, and deliberately oriented towards, offshore financial logics. Offshore urbanism emerges from the convergence of two interrelated dynamics. First, it builds on the long‐standing role of spaces of exception within global capitalism. Second, it reflects the deepening financialisation of the global economy, in which offshore finance has become a central component. Drawing on empirical fieldwork and a critical engagement with the literature on financialisation, spaces of exception and transnational urbanism, this article shows how urban planning strategies actively produce regulatory, material and institutional environments tailored to offshore financial flows. The analysis demonstrates that offshore urbanism aims to ‘plug’ specific urban spaces into the grey circuits of global finance, thereby allowing national and transnational elites to circumvent structural constraints on economic development and to renew strategies of capital accumulation. In Cambodia, offshore urbanism is deeply embedded in a neopatrimonial politico‐economic system, where economic opacity, rentier dynamics and weak regulatory oversight are reframed as comparative advantages. The article further highlights how offshore urbanism normalises the entanglement of legal, illegal and illicit economic activities, mirroring the operational logics of offshore financial centres. Ultimately, by hypothesising that offshore finance is increasingly emerging as a reference model for urban planning, this article sheds light on the underground logics of planetary urbanisation, which remain largely understudied in the academic literature.\n"]