Between 2010 and 2015, the Green Party went from being an james.dennisonafterthought in British politics to an established member of the second tier of Britain’s party system. Although their 2015 election result disappointed many, the “Green Surge“ in membership from late 2014 onwards turned them into the third largest party in England and Wales. Monica Poletti and James Dennison explain the surge did not alter the party’s ideological composition but instead reinforced earlier movements to the left. The Green Surge also created a more balanced membership profile in terms of gender, education and social class. But while most of the party’s members voted for the Greens, one in five of these “surgers” did not, raising questions as to the durability of their membership