Exploring the significance of their role and status in the constitutionalist approach to international law, this chapter will proceed in four steps. The first section (1) will give a short account of the basic features of the constitutionalist approach. Subsequently, possible interfaces between international constitutionalism and subjects doctrine will be explored. It will become apparent that the impact of new participants in the international legal system is ambivalent for a constitutionalist perspective (2). The third section (3) will then ask how non-state actors can nevertheless be accommodated in a general concept of international legal personality as members in the global constitutional community. Considering an important objection to international constitutionalism, it will finally be stressed that, from a normative point of view, participation of affected individuals is a necessary feature of constitutionalization (4).