Discrimination is among the most pressing humanitarian issues that arise in all types of armed conflicts and in different spheres of warfare – be it in the treatment of persons in the power of a Party to an armed conflict or in the conduct of hostilities. International law applicable to such situations, in particular international humanitarian law (IHL) and international human rights law, include important safeguards against such practices. The PhD thesis examines the legal framework to clarify the applicability and scope of relevant rules, as well as their interplay in armed conflict. It also looks at the notions of discrimination, adverse distinction and equality, and their constitutive elements as shaped out by the State practice, jurisprudence of international courts and tribunals and legal scholarship, in order to provide clear legal parameters to draw the line between prohibited discrimination and other differentiations that may be lawful or even required by international law.