Acquisition of territory by force, once permitted, is strictly forbidden today. However, this normative shift has not led to a reconceptualization of annexation, which is still understood as the extension of sovereignty through formal state acts. Maintaining the requirement of formal state acts, we argue, undermines the norm and is further analytically flawed and generates a rule-of-law problem: it fails to capture instances of undeclared annexation, and incentivises states to avoid formal proclamations of annexation to evade legal consequences. This article therefore proposes a new theory of annexation. Drawing on theories of bureaucracy and administration, we suggest three qualifications for annexation: the normative organising framework with which the state manages the territory reflects a perception of the territory as part of its own; the organisational structure of control assimilates the management of the territory into the bureaucratic machinery of the state; and the symbolic performance of power erases symbolic differences between the territory and the annexing state. This reconceptualisation of annexation may support the goal of the contemporary international legal order to suppress aggressive use of force and ensure the self-determination of peoples.