This paper studies human-capital formation, labor-supply, and retirement decisions associated with four alternative regimes of social security. We implement a theoretical model with overlapping generations of households and two different ability types within each generation. We find that with a given social security contribution rate, it is better to transfer income to the elderly as old-age benefits, paid independently of labor-market status. This holds with both Bismarckian and Beveridgean benefits. With sufficiently small ability differences, a Bismarckian system of old-age benefits is likely to offer the highest level of utility to all citizens.