[Excerpt] This report provides a brief overview of the concept of life expectancy, how it is measured, and how it has changed over time in the United States. While life expectancy may be studied in a variety of contexts, this report focuses on the link between life expectancy and SES, as measured by lifetime income. In particular, this report synthesizes recent research on (1) the life expectancy gap by income and (2) the relationship between this gap and Social Security benefits. Finally, this report discusses the implications of this research for one type of Social Security reform proposal: increasing the Social Security retirement age.