This Briefing Paper examines major sources of income for older Americans—earnings, Social Security, pensions and assets—by gender and marital status. It shows that during retirement, Social Security is the most common and the largest source of income for both women and men. Approximately 90 percent of women and men 65 and older receive income from Social Security. During the retirement years, however, women face greater financial insecurity than men. Women tend to marry men who are older than themselves and live longer than men. As a result, women are much more likely than men to be widowed and live alone, making them highly vulnerable to economic insecurity. Having less access to other sources of income, women rely on Social Security even more than men do.