This chapter examines the origins, functions, and consequences of extraterritoriality in Siam, and its important role in the creation of the modern Thai state. It traces the role of extraterritoriality in the creation of a territorially bound polity governed through bureaucratic mechanisms displaying a high degree of legalisation of social relations and integrated into a global capitalist system. The chapter also examines the establishment, operation, and abolition of extraterritoriality in Siam, having as main reference-point the 1855 Bowring Treaty and the subsequent legal, institutional, and economic reforms enacted by the Siamese monarchy in its attempt to have extraterritoriality abolished. It discusses the process of creating a territorialised, centralised state and the assumption of control over former vassal states by Bangkok. The chapter argues that extraterritoriality treaties in 1874 and 1883 crystallised the alliance between foreign capital and the Siamese ruling classes, an alliance that drove the process of state-building in Siam.