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. At the same time, governments are aware that they must maintain taxpayer's faith in the integrity of their tax systems to fund public spending. Fairness and simplicity have become the byword of reformers, but the double challenge has meant that no clear consensus has emerged on an ideal personal income tax. Although there are large differences in tax policies between OECD countries, almost all the reforms of personal income tax in the last two decades can be characterised as rate reducing and base broadening. This study examines the general trends in the taxation of capital income and of 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. The general way ahead will be set by the degree of success of the multiple experiences and policy mixes described in this analytical and comprehensive study.