The incomes of American families change frequently. Some of the poor get richer, some of the rich get poorer, and for a variety of reasons: accumulation of job skills and experience, marriage and divorce, job change, addition or loss of a second paycheck, and business success or failure. But despite this churning, overall rates of mobility in the United States have not changed over time. Thus, it is fair to conclude that increases in annual inequality have worsened the distribution of lifetime incomes. Although the disparity in economic rewards has increased, the availability of those rewardsthe probability of success or failurehas remained unchanged.