EU law revisions and legislative drift

European Union research has made great strides in understanding the dynamics of the European Union decision-making process. In contrast to this progress, the dynamics unfolding after the enactment of a European Union secondary legislative act has largely been ignored. Some of these acts remain in force in their original form for several years while others are revised soon after their enactment. What factors account for this variation? We empirically analyze the proposition that in the presence of 'legislative drift,' i.e. the intertemporal variation of decision-makers' preferences, major revisions of European Union legislative acts are more likely to occur. Based on an analysis of the revision histories of 158 major European Union acts in the time period between 1958 and 2003, we find significant support for this hypothesis.