Budgeting is a rule-driven process that regulates the raising and spending of public money. Detailed rules govern the submission of bids for resources by spending units, review of these bids by the Finance Ministry or another central organ, compilation of the annual budget, legislative action including the voting of appropriations, expenditure of funds during the financial year, and reporting on financial stocks and flows. Why have many national governments adopted new budget rules when they have a plethora of old ones? The new rules do not replace - although they may modify - existing rules, thereby adding to the complexity of established budget processes, and often adding as well to the time it takes to complete the main steps in the annual budget cycle. Why add to the complications of an already difficult process? If it is because the old rules do not work, why is it expected that new ones will make much of a difference? Furthermore, the old rules generally empower budget-makers by enabling them to allocate resources according to the preferences of government. Fiscal rules, by contrast, constrain budget-makers, taking away much of their authority to decide aggregate revenue and spending policy. These rules typically prescribe the balance between revenue and spending policy. Every fiscal rule is a limit on the exercise of political will. Why have democracies accepted or imposed fiscal limits on themselves, and why should we expect these limits to be effective when they run counter to the preferences of voters and politicians?...