This chapter examines the contextual elements of article 2(4) of the UN Charter and the requirement that a prohibited ‘threat or use of force’ be in ‘international relations’. It analyses the meaning of this term and whether it requires that the object of a prohibited use of force be another State and draws conclusions about the types of acts that fall within and outside the scope of this term (and thus the scope of article 2(4)). The type of acts discussed include use of force on another State’s territory or against its extraterritorial sovereign manifestations, to reclaim disputed territory not within de facto control, those in violation of international demarcation lines, those directly arising from a political dispute between States, use of force by a State within its own territory against its own population, in the exercise of law enforcement jurisdiction against private foreign actors, against entities falling short of Statehood, those with no nexus to another State (such as against an international organisation or on terra nullius) and the use of force within a State’s own territory against small-scale incursion by another State’s armed forces.