The article addresses a long-standing debate among economists over what is known as the fiscal multiplier effect. The author reviews a body of recent theoretical and empirical literature on the subject. The latest global financial crisis has led to a renewed interest in the role of discretionary fiscal stimuli, Lubiński says. He adds that the need for fiscal expansion was particularly acute because monetary policy had driven nominal short-term interest rates down to zero without heading off the contraction. Advocates of discretionary measures argue that government spending can stimulate additional private spending, producing the Keynesian multiplier effect, the author notes. Much of the recent economic debate on the impact of stimulus packages has focused on the size of the government fiscal multiplier, according to Lubiński. Government spending multipliers in the empirically-estimated and widely-cited new Keynesian model are much smaller than in old Keynesian models, the author says. Because of uncertainty, he adds, it is essential that policy evaluations are robust to alternative assumptions. Studies suggest that fiscal multipliers are typically positive but small, and while there is some evidence of negative fiscal multipliers, there is no clear consensus on the preconditions for such an outcome. The impact of government expenditure shocks depends crucially on key country characteristics, such as the level of capacity utilization, the exchange rate regime, openness to trade, public indebtedness, household behavior, and the crowding-out effect. Moreover, the effects of fiscal packages are nonlinear, Lubiński notes. As a result, the fiscal multiplier is an uncertain guideline for stabilization policy, the author concludes.