In July 2010, the International Court of Justice rendered an Advisory Opinion on the conformity of the unilateral declaration of independence of Kosovo with international law. The paper examines the contribution of this opinion to the constitutionalization of international law....

This paper shows that three versions of the principle of proportionality exist in international law, and that these three have different constitutional functions. The horizontal version 1 applies, inter alia, in the field of countermeasures including self defence. The principle here refers to...