This chapter describes the diversity of data on British party members, gathered over a number of decades. When it comes to political opinions, the findings broadly conform to people understanding of Britain's party system, with the Conservatives representing one extreme, the Greens another and the other parties located in between. The study of party membership and activism in Britain is well established and genuinely pioneering. In 2013, the Conservatives and Liberal Democrats adopted a simple approach to membership subscriptions, with only three fee categories. The other parties, however, vary membership rates according to quite specific characteristics, from low-income groups and members of the armed forces to joint membership, overseas status and lifetime membership. Declining voter loyalty to the main parties, and the rise of relatively new parties like the Greens and the United Kingdom Independence Party (UKIP), have made their mark on British politics, giving the party system more of a multi-party character.