Whilst most legal scholarship focuses on the responsibility of the United Nations for human rights violations few studies have ascertained the legal basis of the primary rules leading to such responsibility. This article fills this gap by reviewing the theories used to bind the UN to customary human rights law: (1) the UN has inherited its Member States’ obligations, (2) participation in the formation of customary human rights law implies being bound by it, (3) the UN is bound by international law because it has legal personality and (4) as the UN is embedded in international law it must comply with its norms. Such theories are further tested against the backdrop of international organisations’ theories. The article draws the conclusion that (1) should be rejected, (2) is not yet legally sound and (3)-(4), despite their flaws, are more persuasive. Ultimately, recourse must be had to the general international law.