Summaries The author examines aggregate and categorical fungibility for the recipient of untied foreign exchange. Aggregate fungibility considers the impact of the funds received on either external account aggregates such as imports or exports, or the overall level of revenue, expenditure and government borrowing. Analysis of categorical fungibility looks inside the item of most interest to the donor (import composition in the case of import support and sectoral expenditure for counterpart funds and budget aid). These questions are best answered by macroeconomic modelling, but the data are rarely available. Hence a more ad hoc approach must be used. Aggregate fungibility may be analysed through the construction of a counterfactual balance of payments and government budget, where behavioural reactions are judged by the evaluator on the basis of own analysis, existing studies and guestimates. Categorical fungibility may be analysed using the budget constraint approach in conjunction with a counterfactual government budget.