In contemporary representative democracies, political competition is not only taking place between political parties but also within parties. Hitherto, research on such intra-party competition has been mostly focused on the electoral dimension, mainly looking at the distribution of preference votes among co-partisans running on the same party list. In this introduction to our symposium on intra-party competition, we argue that intra-party competition occurs in other stages of the electoral cycle than elections and involves the strategic behaviour of more actors than electoral candidates. We present an original conceptual model that introduces a multi-stage and multi-actor perspective on intra-party competition, including three stages (the nomination stage, the electoral stage and the post-electoral stage) and three key actors (voters, politicians and parties). Based on our novel conceptual model, we provide examples of strategic behaviour of each actor in each of the stages. We further introduce each contribution of this symposium and present how each contribution relates to our multi-stage and multi-actor model of intra-party competition.