This study argues that customary international law obliges the Baltic states to accept the Slav populations as an integral part of the Baltic peoples. The history and collapse of the Soviet Union has produced large groups of Slav immigrants to remain in the Baltic states. They are not automatically granted citizenship rights in Estonia and Latvia, as they have to prove to qualify for naturalisation. People descending from the inter-War citizenry do ipso facto qualify for citizenship. First the nature of the coming-to-independence of the Baltic states is analysed, after which the law on self-determination is investigated. The de facto recognition of the Soviet annexation by most of the international community is seen as the watershed as far as the status of the Baltic states is concerned; from then on they were for all practical purposes part of the Soviet Union. Following an analysis of the applicable norms of customary international law, a scrutiny of relevant Baltic legislation is presented.