As Social Security reform is considered in the United States, one of the recurring issues is likely to be the impact on women of various proposed changes. This Policy Brief summarizes the reasons why the same pension system may have quite different effects on men and women, why a given pension reform may have an inadvertent gender impact, and what policy choices can affect these outcomes. It draws on research that evaluates the gender impact of the new pension systems in Chile, Argentina and Mexico, compares the Latin American systems with recent reforms in the transition economies and Sweden, and discusses implications for the United States.