This paper is the result of a collaborative research project sponsored by the Rockefeller Foundation, the Russell Sage Foundation and the European Science Foundation as part of its Network on Household Panel Studies. CEPS/INSTEAD provided substantial in-kind support. Deborah Laren provided excellent research assistance. Jos Berghman, Tim Callan, Bengt-Olof Gert, Peter Gottschalk, Pierre Hausman, Bruno Jeandidier, Kjell Janssen, Stephen Jenkins, Anders Klevmarken, Katherine McFate, Udo Neumann, Willard Rodgers, Gaston Schaber, Tim Smeeding, Daniel Stripinis, Hedwig Vermeulen, Wolfgang Voges and Brendan Whelan provided substantial assistance and advice during the course of the project. An earlier version of the paper was presented at the conference “Poverty and Public Policy” in Paris in January, 1991. The paper was edited by Timothy M. Smeeding, Syracuse University, using two anonymous referees.