To compare parliamentary capacity for financial scrutiny, I construct an index using data for 36 countries from a 2003 survey of budgeting procedures. The index captures six institutional prerequisites for legislative control, relating to amendment powers, reversionary budgets, executive flexibility during implementation, the timing of the budget, legislative committees and budgetary information. Various methods of index construction are reviewed. The results reveal substantial variation in the level of financial scrutiny of government by the legislature among contemporary liberal democracies. The US Congress has an index score that is more than three times as great as those for the bottom nine cases, predominantly Westminster systems. Even allowing for US exceptionalism, the top quartile of legislatures score twice as high on this index as the bottom quartile. These findings suggest that the power of the purse is a discrete and non-fundamental element of liberal democratic governance. For some countries it is a key safeguard against executive overreach, while others maintain a constitutional myth.