Zero-based budgeting (ZBB) is a budgeting approach requiring every expense to be justified from zero each budget cycle, rather than simply adjusting previous year amounts. Traditional incremental budgeting starts with last year's budget and makes marginal changes; ZBB theoretically starts fresh, requiring departments to justify their entire budget. ZBB proponents argue it prevents budget 'drift' where programs continue indefinitely without reassessment. Critics note ZBB is extremely time-consuming and may not be practical for large organizations or ongoing essential services. Few governments apply pure ZBB, but elements—like periodic program reviews or base budget reviews—incorporate ZBB concepts. ZBB can be useful for examining specific programs or departments without applying it organization-wide. The approach enjoyed popularity in the 1970s and has seen periodic revivals.