International humanitarian law (IHL) does not provide a precise definition of the notion of occupation, nor does it propose clear-cut standards for determining when an occupation starts and when its ends. This article analyses in detail the notion of occupation under IHL and its constitutive elements, and sets out a legal test for identifying when a situation qualifies as an occupation for the purposes of IHL. It concludes by suggesting an adjustment of the legal test to the specific characteristics of occupation by proxy and occupation by multinational forces.