The likely effects of the ongoing process of European integration on the internal workings of national political parties have hitherto attracted surprisingly little attention in comparative research. This conceptual article discusses how the increasing relevance of European-level decision making may have changed the balance of power within national political parties. It identifies two groups of party actors who are most likely to benefit from the process of Europeanisation of national political parties. First, the ‘executive bias’ of European Union (EU) decision making is likely to work in favour of party elites in general. However, while they may gain power in intra-party decision making, their control over the national policy agenda is likely to become increasingly eroded through a general shift of policy control to the European level. Second, EU specialists (i.e., those who specialise in EU affairs) are likely to have more access to resources and more control over policy decisions within national parties because of the growing importance of European integration. These propositions are discussed in detail and are then assessed with reference to the main findings from a major empirical study of the topic.