While Greens in the UK have always suffered from a grossly unfair electoral system, in the European Union they have been able to flourish as part of a small but effective group of European Greens since their first election in 1999. Greens have had a significant influence on the policies impacting more than 500 million EU citizens, underlining environmental standards and challenging economic and social orthodoxy. While Greens have often been marginalised by the political and media elites in Britain, across Europe, Greens have been seen as 'the voice of reason' and the 'adults in the room'. With Brexit threatening our ongoing influence on European policy-making, former and current UK Green MEPs Caroline Lucas, Jean Lambert, Keith Taylor and Molly Scott Cato reflect on their time in Brussels and chart a course for the party's new relationship with the EU-wide Green movement. This guide to two decades of UK Green achievements in Europe also brings together analysis from prominent academics, journalists, campaigners and Green MEPs from across the EU.