This chapter addresses the subject of the legal limitations which international law places on the imposition of international economic/financial sanctions, with particular reference to sanctions with counter-proliferation aims. It argues that there are at least three sources of international legal obligations which impose limits on the application of coercive international economic/financial sanctions: (1) the general international principle of noncoercion, (2) the law of countermeasures, and (3) human rights law. The totality of these obligations limiting the lawfulness of both unilateral and multilateral coercive sanctions purposed in counter-proliferation leaves a vanishingly small window for the lawful application of such sanctions.