The most significant economic and social change in the past half-century has been the movement of women into the labor market. Since the 1950s, the labor participation rate of women ages 25 to 55 years has increased more than 75 percent. Today, more than 60 percent of mothers with children under the age of six are working. Families with both spouses in the labor market now constitute almost two-thirds of all married couples. Yet the tax law, pension law, social insurance policies and laws governing employee benefits assume women never left the home.