Although there is fierce debate about how best to evaluate the effectiveness of international regimes, most writers regard institutional effectiveness as the best measure. This article examines the institutional effectiveness of one regime-the Barcelona Convention (or the Mediterranean Action Plan)-where there are sharply contrasting views of its institutional effectiveness. The study finds that the regime was indeed successful when created, but its contemporary institutional performance is inadequate. The article demonstrates that there is no simple answer as to whether a regime is effective; instead, in most cases it depends on the specific criteria each approach employs. © 2007 Elsevier Ltd. All rights reserved.