We are grateful for the assistance and encouragement given by our colleagues Anthony B. Atkinson and Lee Rainwater as well as the large number of country experts who provided useful comments on earlier drafts and participants at seminars at Princeton, Rand, Stanford, and U.C. Berkeley. Support for this project was provided for Smeeding by the Russell Sage Foundation and by NSF #SBR-9511521. Helpful comments were received from several referees, Anthony Atkinson, Anders Bjorklund, Gary Burtless, Sheldon Danziger, John Fitzgerald, Johan Fritzell, Joop Hartog, Markus Jantti, Stephen Jenkins, Robert Lerman, John Myles, Robert Plotnick, James P. Smith, and Peter Saunders. Esther Gray, Katherin Ross, and Ann Wicks provided excellent assistance with the manuscript. The authors assume responsibility for all errors of commission.