This volume contains selected contributions from the European Cluster Days 2015, which took place in March 2015 in the European Parliament in Strasbourg. The conference was organised by France Cluster, which is the network of French cluster initiatives, and the European Competence and Research Center for Cluster Management, which is an institute of the University of Strasbourg, Department of International Relations Studies (France), the University of Applied Sciences Kehl (Germany) and the University of Applied Sciences and Arts Northwestern Switzerland. Almost 400 experts and researchers enjoyed an excellent opportunity for meaningful dialogue at the conference. Could clusters become the growth engines in the European economy?