Parliamentary procedure has largely been neglected as a constraint on government. Political developments in the UK and a (contested) scholarly focus on institutions provide the basis for re-evaluating the consequences of procedure in the British Parliament. Procedure in both Houses of Parliament is well established and institutionalised. The capacity of procedural rules to constrain government is illustrated though empirical examples. Rational-choice theory and historical institutionalism are utilised to explain why rules endure, despite government having the political resources to change them. The 'price' of change can be too much for government in terms of time and intellectual resources, in terms of future prices and in terms of legitimacy. Consequently, procedure matters.