The Spanish system of territorial autonomies has reached a crossroads. After over thirty years of development, the consensus regarding its appropriateness has started to crumble. The transformation project embodied by the reform of the Statute of Catalonia (2006) has failed to achieve its most significant aims. Although the concept of Spain as a federation is disputed - more within the country than beyond -, the evolution of the Spanish system needs to follow a markedly federalist path. In this perspective, reference models take on critical importance. This book gathers the works of a broad group of European, American and Spanish experts who analyse the present-day challenges of their respective systems in terms of the distribution of power (competences), inter-governmental relations and the integration of diversity, the objective being to contribute ideas which might help to address the evolution of the Spanish system in light of the experience of more established federal systems.