This chapter describes Art 2 (4) of the UN Charter. Article 2 (4) provides that ‘all Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the purposes of the United Nations’. The chapter outlines pre-Charter rules against force, highlighting that Art 2 (4) marked a new beginning, and summarizes the drafting history of the provision. It also analyses the scope and normative context of Art 2 (4). This attempt must remain selective, but it covers three central aspects: the relationship between the ban on force and its exceptions; the status of the ban as a customary rule of jus cogens; and core features of the legal regime governing breaches of Art 2 (4).