In the Rome Statute, and more generally in international criminal law, the principle of ne bis in idem is not solely concerned with the promotion of the rights of the accused or the res judicata authority of a first judgment. It seems to be also - maybe primarily - dedicated to articulating the concurrence between national and international jurisdictions. The present article discusses its different functions, asserting that they differ whether the principle intervenes in an intra- or inter-jurisdictional situation. It also links these functions to the general struggle against impunity governing international criminal law, and concludes by striving to attribute a structural, possibly qualitative role to the principle. © Oxford University Press, 2011, All rights reserved.