One observation about the budgets of governments has passed into the conventional wisdom: budget-making, we are told, is a process of ‘incremental decision making’. The approach of the incrementalists is directed primarily to the question of how the creation of the new budget in a particular year (‘the budgetary process’) is to be explained. The approach seeks to characterize how budgeters respond to the problem of allocating resources and to develop explanatory models of budgetary outputs. But, despite the volume of research that now exists on budgetary incrementalism, the operationalization of the concept remains an issue, and many of the empirical studies have the limited perspective of a single budget-making system – that is, of one set of resource allocators, who employ the same standard operating procedures, rules of search, and so on. This paper has two objectives: (1) to explicate some simple operational models of budgetary incrementalism; and (2) to examine the adequacy of these models by means of an empirical test in four comparable budget-making systems – British county boroughs.