This chapter provides a case study in regulatory multi-level governance within the European Union, with a substantive focus on the regime in place for the authorisation of cultivation of genetically modified crops. Whilst presenting a detailed account of the supranational level regime, it seeks explicitly to write in the subnational, regional dimension to our accounts of policy evolution in this highly controversial area. The chapter considers regions’ ‘upstream’ engagement in the policy processes at EU level, through judicial challenge to EU measures as well as attempts to influence supranational level legislative reform, which is currently ongoing. In this regard, it looks both at the role of regions within this process, and within the terms of the resultant legislation. In addition, the chapter considers regions’ ‘downstream’ engagement, in their implementation and application of the existing rules. As a number of regions have sought to declare themselves GM-free zones, this chapter explores the legality of such local and regional GM crop cultivation bans, as a matter of EU law. In short, the chapter contributes further to our understandings of the place held by regions within the EU system of governance demonstrating how regions may themselves be both legal and political actors of significance within the EU order, whose interests are not always congruent with that of their Member State.