Studies of the United Kingdom's decision to leave the European Union ("Brexit") have largely focused on the role of politicians and political parties, on the one hand, and the characteristics of Leave and Remain voters on the other. The Failure of Remain offers the first comprehensive study of the UK's grassroots anti-Brexit movement. Emerging in the weeks and months following the June 2016 referendum, this movement was the most significant and wide-scale mobilization of pro-European support that the UK had ever witnessed. In The Failure of Remain Adam Fagan and Stijn van Kessel assess participants' ideologies, arguments, and strategies. Drawing evidence from first-hand interviews, an original survey of anti-Brexit activists, and an analysis of their campaign materials, Fagan and van Kessel conclude that while the anti-Brexit movement was successful in mobilizing a large number of pro-European citizens, its impact was limited by weak links to political elites and institutions, divisions between organizations and activists, and the absence of a clear stance on the UK's relationship with the European Union. In the context of enduring debates about the future direction of European integration, The Failure of Remain reveals the difficulties of formulating effective pro-European arguments.