This article examines different views of the European Union (EU) legislative decision-making process through a quantitative analysis of all Commission proposals initiated between 1984 and 1999. Using the positions of Member States, the analysis is innovative in two respects: the identification of the relative importance of institutions and preferences for the process of EU legislative decision making, and the empirical evaluation of the ongoing theoretical controversy between constructivists and spatial analysts about the converging or diverging effect of Member State positions. The findings reveal that the process of EU legislative integration is significantly slowing down, even though Council qualified majority voting facilitates decision making while parliamentary participation modestly increases the duration. Against the constructivist claims of convergence, the results show that the divergence of Member State positions significantly determines the duration of the legislative process, in particular in the key domains of EU integration: the larger the distance between the Member States' positions, the longer the EU decision-making process takes. This suggests that the accession of countries with diverging positions will slow down the EU's legislative process, but institutional reform of the Council's decision-making threshold is a promising solution for coping with this effect.