The chapter examines the interplay between competitive solidarity and regional development through the case study of the Italian Mezzogiorno. In response to a persistent lagging behind of Southern regions, the Italian state (since 1950) and the European Union (since the 1970) have deployed regional policies of varying intensity, focus, and institutional design. These have benefitted the Mezzogiorno with important flows of public investment and social spending, but they have failed to reduce its developmental gap in relation to the rest of the country. The main causes of this failure are multiple, including the overall weakness of national development over the last decades, insufficient resources, the lack of linkages with wider supporting policies and reforms, policy design flaws, political problems, and a weak administrative capacity. Overall, the current policy phase (2014–20) has contributed to a further weakening of the coherence of Italian regional development policy, as well as of its economic and social achievements.