Regionalist parties matter. Over the past 40 years, they have played an ever-larger role in West European democracies. Because of their relevance and temporal persistence, their achievements have increasingly become visible not only in electoral arena, but also as regards holding office and policy-making. Enhancing our understanding of these different dimensions of success, this book analyses various types of regionalist party success. Beyond conventional perspectives, the focus of this book is also on how the dimensions of success are related to each other, and in particular to what extent electoral and office success – jointly or alternatively – contribute to policy success. Adopting a common theoretical framework and combining the in-depth knowledge of country experts, each chapter explores the evolution and impact of regionalist parties in regional or federal states, that is the UK, Germany, Italy, Spain, Belgium, and Switzerland. This allows for a comprehensive and comparative analysis of one of the main political challenges within West-European democracies.