This chapter examines Switzerland’s constitutional and legal foundations, especially Article 70 of the Federal Constitution, and the logic of the territoriality principle. It explains how linguistic rights are allocated not to individuals but to regions, producing a system in which multilingualism is formally recognized at the national level but implemented through largely monolingual cantonal structures. The chapter analyzes how this principle has historically stabilized linguistic coexistence yet now struggles to accommodate increased mobility, demographic change, and fluid linguistic practices. The discussion highlights tensions between federal ideals of harmony and the administrative realities of regionally bounded monolingualism. Drawing on Shohamy and Spolsky, the chapter shows how the territoriality principle functions as a policy mechanism, shaping who may use which language where, and under what conditions. It further reviews research on where territoriality has produced stable arrangements and where it has encountered friction, particularly in multilingual cantons such as Grisons. Ultimately, the chapter argues that the territorial model sustains linguistic peace while limiting individual linguistic freedom and obscuring new forms of multilingual belonging.