This article develops an attention-based model of party mandates and policy agendas, where parties and governments are faced with an abundance of issues and must divide their scarce attention across them. In government, parties must balance their desire to deliver on their electoral mandate (i.e. the ‘promissory agenda’) with a need to continuously adapt their policy priorities in response to changes in public concerns and to deal with unexpected events and the emergence of new problems (i.e. the ‘anticipatory agenda’). Parties elected to office also have incentives to respond to issues prioritized by the platforms of their rivals. To test this theory, time series cross-sectional models are used to investigate how the policy content of the legislative program of British government responds to governing and opposition party platforms, the executive agenda, issue priorities of the public and mass media.