This article analyzes the coexisting meanings, interpretations and functions underlying the varying uses of immigration detention in Swiss cantons. The authors argue that cantonal immigration bureaucracies decide on administrative detention according to different and intertwined implementation rationales, revealing varying functions and reasonings which shape its uses in practice. This highlights the significant variation in subnational policies and practices with regards to immigration detention within a single federal country, depending on these rationales and the cantonal contexts. The cantonal discretionary implementation of the same legal norms leads to various cantonal policies, resulting in different numbers and profiles of persons detained.