This volume aims to provide a general overview of the processes of democratic innovation within political parties. In practice, this has led to an in-depth examination of the introduction of primary elections. The need for a comparative analysis on this topic is a result of the recent spread of inclusive procedures for recruiting political personnel in parties outside the United States. Over the last two decades, a growing number of parties have introduced primary elections for selecting candidates and leaders, including Belgium, Italy, France, Romania, Slovakia and Iceland. Beyond Europe, intra-party democracy also has improved in Israel, Canada, Japan, Taiwan and South Korea, not to mention in various Latin American countries. Many parties in these countries promote participative opportunities involving their members, or even the entire electorate, to choose candidates for public office and party leadership. Nevertheless, despite recent trends towards involving activists and voters in parties’decision-making, analysis of the implementation of primary elections outside the US is not equally developed. There is also a lack of analysis on the impact of these intra-party reforms at electoral and organisational level. If anything, the few studies on primaries outside the US have underlined the differences from the American case taken as a reference, providing a framework of analysis which now needs to be supported by empirical research.