This chapter proceeds in three steps. I first briefly outline the principal theories that justify secession. Next, I analyze the evolution of secession in international law and in international practice, as a corollary of the right of all peoples to self-determination. Finally, in the last Section, I turn to the relationship between secession and constitutionalism and ask whether the constitutionalization of the right to secede can, in particular context, be regarded as a constructive response to secessionist challenges and what its implications are for constitutional law.