Over the last three decades, European Union regulation of the internal market has become highly pervasive, affecting practically all domains of European citizens' lives. Many studies have focused on understanding the process and causes of regulatory change, but with limited attempts to analyse the more general sources of regulatory reform. This article focuses on the determinants of stability and change in EU regulation. An original dataset of 169 pieces of legislation (regulations, directives and decisions) across eight different sectors is developed and the dynamics of regulatory reform in the EU are analysed. Using time-series analysis of count data, evidence is found that the number of winning coalitions in the Council and the size of EU membership have a significant impact on regulatory reform in the EU. By contrast, the ideological composition of the EU's legislative bodies is not systematically related to regulatory reform.