On February 25, 2019, the International Court of Justice issued its advisory opinion on Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965. The judges held by a majority of 13:1 that the process of decolonisation of Mauritius is incomplete, owing to the separation of the Chagos Archipelago shortly before Mauritian independence, that the United Kingdom should end its administration of the Chagos Archipelago as rapidly as possible, and that all Member States of the United Nations should cooperate to complete the decolonisation of Mauritius. The (partial) decolonisation of Mauritius in 1968 and the treatment of the Chagos islanders (Chagossians) have important parallels with the purported decolonisation of Greenland in 1952–54. In both cases, the consultative body of the colonised people was neither fully independent nor representative of all the people concerned. No real choice was given to either body; rather the colonial power offered only the continuation of the status quo or professed self-determination on terms defined by the colonial power itself. Furthermore, the process of decolonisation was inherently linked to the forcible transfer of people in order to make way for a United States military facility. Nevertheless, there are some relevant differences. First of all, Greenland was purportedly decolonised in 1953, some seven years before the UN General Assembly Declaration on the Granting of Independence to Colonial Countries and Peoples (UNGA Res. 1514(XV) 1960). Second, the UN General Assembly accepted the Danish government’s representations regarding the full decolonisation of Greenland (UNGA Res. 849 (1954), in contrast to their position regarding Mauritius that decolonisation was and remains incomplete, owing to the separation of the Chagos Archipelago (UNGA Res(XX) 1965). Third, though the Chagossians have been recognised as indigenous at the UN, the British government has continually denied this status and (mis)characterises them as a transient people, while Denmark has accepted the status of the Greenlanders as both an indigenous people and a colonial people, entitled to self-determination. This article examines the implications for the judgment for the Greenland case as well as broader questions of self-determination of peoples. It concludes that the colonial boundaries continue to govern in decolonisation cases, with the consequence that the Greenlanders are likely to be held to be a single people; that the erga omnes character of the right to self-determination means that all States must cooperate to facilitate Greenlanders’ choices for their future; and that there remain significant procedural hurdles that prevent colonial and indigenous peoples having their voices heard, even in the matters that concern them most of all.