Social security systems are being reviewed and changed in many countries around the world. This nontechnical book considers some of the key policy issues for design of a social security reform, as well as reviewing much of the academic literature on the positive and normative aspects of social security. In the first chapter, Diamond's examination of key policy issues of general concern includes the funding of social security, the comparison of defined benefit and defined contribution systems, notional defined contribution accounts, alternative approaches to organizing individual defined contribution accounts, and the provision of survivor benefits. Diamond turns then to the academic literature on the interactions between social security and the labor and capital markets, providing a non-technical overview of the existing literature and pointing-out gaps in current research findings. Chapter Two reviews the impact on retirement decisions of forced savings, the use of an earnings or retirement test, mandated annuitization, recognizing heterogeneity in both life expectancy and possibly in risk classification for annuity pricing, and treatment of the family, particularly the use of joint-life annuitization. Also reviewed is the impact on labor supply at younger ages, considering mandatory savings and annuitization, contrasting defined benefit and defined contribution systems, and analysing alternative approaches to redistribution within social security. The final chapter covers issues of aggregate capital accumulation and risk-sharing, with the latter including the risks in annuitization, in the returns to capital, and in aggregate earnings. Also considered are the risks in the political process.