In a drive to encourage risk-taking, entrepreneurship and competitive fiscal advantage, many OECD countries have reformed their personal income tax system fundamentally over the last two decades, generally in ways that can be characterised as rate reducing and base broadening.  This comprehensive study examines the general trends in the taxation of capital and wage income, and the most significant changes that have taken place. It looks closely at the main drivers of reform, the trade-offs between policy objectives, the guidelines, objectives and design features of tax reforms and why fundamental reform of personal income tax systems has been so high on the agenda. The principal systems of taxes on personal capital income and wage income - comprehensive, dual and flat – are thoroughly examined and evaluated in the OECD countries that have adopted these different systems or a mix thereof.  They are each assessed in terms of the fundamental principles of sound tax policy: simplification, efficiency, equity, tax compliance and tax revenue, and their main advantages and disadvantages are discussed.