The literature on budgeting in the public sector has traditionally focused on the annual budgetary process. Much less attention has been paid to rebudgeting—that is, what governments do to revise and update their budgets during the fiscal year. Because of its potentially large impact on appropriations, rebudgeting seemingly deserves more attention than it has been granted so far. This article uses data from a sample of Italian municipalities to test hypotheses on the main drivers of budget revisions. According to the results, rebudgeting is strongly affected by the degree of incrementalism in the initial budgeting process, as well as by several internal and external determinants, such as political variables, organizational features, financial conditions, and the local socioeconomic environment.