This dissertation comprises two essays that attempt to determine, empirically, the relationship between personal income taxation and income inequality. The first essay examines whether income inequality is affected by the structural progressivity of national income tax systems. Using detailed personal income tax schedules for a large panel of countries, we develop and estimate comprehensive, time-varying measures of structural progressivity of national income tax systems over the 1981–2005 period. Our findings suggest that progressivity has a strong negative effect on inequality in reported gross and net income and that this negative effect is strongest in countries whose institutional framework supports pro-poor redistribution. However, the effect of progressivity on true inequality, which is approximated by consumption-based measures of the GINI coefficient, is significantly smaller. The second essay relies on household level data and complements the first in its empirical approach. We simulate the distributional impact of the Russian personal income tax (PIT) following the flat tax reform of 2001 using data from the Russian Longitudinal Monitoring Survey. We use a series of counterfactuals to decompose the change in the distribution of net income into a direct (tax) effect and an indirect behavioral effect. As expected, the direct tax effect increased net income inequality. Changes in the pre-tax distribution, on the other hand, had a large negative impact on inequality thus leading to an overall decline in net income inequality. We also find that the tax-induced evasion response increased reported net income inequality while reducing consumption based measures of net income inequality.