This is the accepted version of the following article: Fisher, J., Fieldhouse, E. and Cutts, D. (2014), Members Are Not the Only Fruit: Volunteer Activity in British Political Parties at the 2010 General Election. The British Journal of Politics & International Relations, 16: 75–95, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/1467-856X.12011/abstract.Existing research on volunteer activity in political parties has tended to focus on party membership, both in terms of numbers and activities undertaken. Recent developments in British political parties suggest however, an increasing role for party supporters—supporters of parties who are not formal members. Using data collected through surveys of election agents at the 2010 general election, this article examines the extent of supporter activity in constituency (district-level) campaigns, the extent to which active local parties stimulate supporter activity, the correlates of supporter and member activity, and whether supporter activity makes a positive and independent contribution to parties’ constituency campaigns. The article provides an important opportunity to question whether the evolution of party organisations suggests that formal members may be less important than has been previously assumed in the conduct of election campaigns and the extent to which supporter activity complements that of members.Economic and Social Research Counci