Electoral politics in the larger western democracies seems to be becoming increasingly ‘denationalised’: non-statewide political parties have grown in strength, and demands for decentralisation have led to major institutional changes in large unitary states in recent years. As a result, the conventional view of party politics as essentially taking place at the national level, between national parties, over national issues, appears increasingly inadequate. This article argues that party scholars need to look more closely at what we could call the ‘territorial dimension’ of electoral politics: the spatial and geographical aspects of party competition. This article presents a preliminary analysis of how centre-periphery tensions and institutional reforms affect the way statewide parties organise, focusing on the areas of elite recruitment, electoral programmes and campaigning, and party behaviour in public office. It hypothesises a variety of patterns of party response, and provides some tentative evidence from Western European democracies, and in particular in Britain, Italy and Spain. This analysis shows that the internal workings of statewide political parties are a key variable in understanding the relationship between institutional reform and the ‘denationalisation’ of electoral politics.