Unequal distribution of income is one of the most important socio-economic issues. The processes of globalisation and integration are accelerating economic growth; however, at the same time, imbalances between regions are growing. Reducing inequalities within regions and national economies, as well as around the world, is important for individual and societal well-being and cohesion, and for effective state policies. This book investigates the problem of left-behind regions in the European Union (EU). It first introduces the reader to the theories of regional imbalances and problems with measuring them. It then explores imbalances in the EU using a variety of indicators and describes the EU’s regional policy for reducing regional disparities. It uses an empirical shift-share analysis to assess the productivity of EU regions which are lagging behind. The book also provides an empirical analysis of the effectiveness of EU funds in increasing labour productivity performed with DEA methodology. This book can be used as a teaching resource for undergraduate and postgraduate students and can serve as reference material for academics and researchers, as well as policymakers at the European, national and local levels.