In this book, we examine the varying ways in which political parties manage intra-party conflict, or potential conflict, when they make what might be their most important decisions – on the selection of their leaders. We take special account of actors that, formally and informally, filter the field of aspirants even before the decision reaches the selectorate. Our analytical framework is developed both deductively, with a foundation in delegation models, and inductively, through reference to case studies from nine European countries. We present a typology of selection processes, which illuminates intra-party power structures.