This unique and important new book looks at how we interpret the evidence of change and stability in modern parties and party systems. Focusing primarily on processes of political adaptation and control, it also concerns how parties and party systems generate their own momentum and 'freeze' themselves into place. Amidst the widespread contemporary discussion of the challenge to modern democracy and the crisis of traditional forms of political representation, it offers a welcome emphasis on how party systems survive, and on how change, when it does occur, may be analysed and understood.