This book analyzes how mainstream and new parties are building their digital platforms and transitioning from traditional (offline) organizations into the digital world. The authors present an innovative empirical exploration of the democratic consequences and technical challenges of the digitalization of party organizations from a comparative perspective. They provide an original account of how party digital platforms are regulated and used, and a crucial discussion of the main technological and democratic issues that political parties face in their digital transition. Further, the authors assess the consequences of these digitalization processes for political participation and party membership, as well as the impact on party organizational models and