This paper illuminates a critical stage of the implementation of European law: the transposition of European Union (EU) directives. Directives must be transposed into national policies in order to give effect to European law, yet most national authorities experience considerable transposition difficulties. For this reason, the study of transposition has become a focal point within the broader research agenda on non-compliance in the European Union. Highlighting several popular explanatory variables but noting the sometimes contradictory results that follow from empirical testing, this paper outlines an approach that views transposition as a process taking place largely within ministerial agencies rather than across government systems. By using variables related to these domestic processes in our empirical analysis, the paper shows how such an approach can help to explain the way in which member states transpose EU directives.