In this article I address the impact of decentralisation on the nationalisation of party systems. Many scholars have argued that when a country decentralises, candidates have greater incentives to compete locally and party system nationalisation is eroded. However, the empirical results are inconclusive, particularly in Western European countries, so it is necessary to revisit this causal link. My argument is that the impact of decentralisation on the nationalisation of party systems is conditional on the extent to which electoral law encourages personal voting. When electoral laws are candidate-centred, party labels are not very relevant in politicians' (re-)election; this makes candidates more likely to compete locally in a decentralised country and to weaken party system nationalisation. Through two different indices of nationalisation and statistical techniques, I test the robustness of this argument by drawing on data from national legislative elections held in seventeen Western European countries. The evidence confirms the main argument as well as the de-nationalising effect of ethnic fragmentation and district magnitude.