Using methods for assessing both correlational causation and necessary/sufficient causation, this article addresses a fundamental puzzle confronting those who seek to understand one important part of the EU policy cycle, namely to explain why member states of the EU differ in their transposition records of EU legislation. Exploring a rationalist framework to assess the transposition problematic in the EU the article treats theoretically and empirically determinants of transposition termination and duration. Using a comprehensive data set on large-scale transposition records in 9 member states (Germany, the UK, France, Italy, Spain, Greece, Ireland, the Netherlands and Sweden) covering the 1995-2004 period, they are tested by means of ordered multinomial logistic and hazard function regressions. Drawing on existing research and knowledge, calibrated measures further improve our understanding of widely acknowledged notions of necessary and sufficient conditions.