This article introduces the collection of articles of the special issue and provides a discussion of the common themes linking these contributions. The article stresses the continuing significance of the Maastricht Treaty and illustrates the various ways in which the key reforms of the early 1990s still matter today. This includes not only the bearing that the decisions at the time of the Maastricht Treaty have had on the current crisis of the Eurozone, but also the developments in the areas of foreign policy and justice and home affairs. Indeed, the very move towards 'pillarisation' as well as key institutional changes such as the creation of the co-decision procedure and the elevation of the European Council all continue to play an important role today. The article concludes with some reflections about the legacy of the Maastricht Treaty, highlighting both the achievements of the treaty but also the shortcomings in terms of enhancing democratic legitimacy and engagement with civil society - indicating the key challenges that the Union still faces today.