This paper investigates whether taxpayers bunch at the kink points of the US income tax schedule, where marginal tax rates jump. Evidence of bunching is found only at the first kink point (where marginal rates jump from 0 to 15%). Evidence for other kink points is weak or null. Bunching is stronger for itemizers than for non-itemizers. Theoretical models show that bunching is proportional to the compensated elasticity of income with respect to tax rates. These models are used to simulate bunching and calibrate key parameters to empirical income distributions. Except for low income earners, the behavioral elasticity consistent with empirical results is small. The paper uses tax return data from 1979 to 1994 to analyze bunching at kink points. It finds that the first kink point (0-15% marginal rate jump) shows clear bunching, while other kink points do not. Bunching is stronger for itemizers. Theoretical models suggest that bunching depends on the elasticity of income with respect to tax rates and the extent to which taxpayers control their income. Simulations show that bunching is more pronounced with higher elasticity and smaller income variability. The results indicate that the behavioral elasticity consistent with empirical data is small, except for low income earners. The paper also discusses the implications of these findings for tax policy and behavioral responses to taxation.This paper investigates whether taxpayers bunch at the kink points of the US income tax schedule, where marginal tax rates jump. Evidence of bunching is found only at the first kink point (where marginal rates jump from 0 to 15%). Evidence for other kink points is weak or null. Bunching is stronger for itemizers than for non-itemizers. Theoretical models show that bunching is proportional to the compensated elasticity of income with respect to tax rates. These models are used to simulate bunching and calibrate key parameters to empirical income distributions. Except for low income earners, the behavioral elasticity consistent with empirical results is small. The paper uses tax return data from 1979 to 1994 to analyze bunching at kink points. It finds that the first kink point (0-15% marginal rate jump) shows clear bunching, while other kink points do not. Bunching is stronger for itemizers. Theoretical models suggest that bunching depends on the elasticity of income with respect to tax rates and the extent to which taxpayers control their income. Simulations show that bunching is more pronounced with higher elasticity and smaller income variability. The results indicate that the behavioral elasticity consistent with empirical data is small, except for low income earners. The paper also discusses the implications of these findings for tax policy and behavioral responses to taxation.