Previous studies, relying on short-term averages of fathers' earnings, have estimated the intergenerational elasticity (IGE) in earnings to be approximately 0.4. Due to persistent transitory fluctuations, these estimates have been biased down by approximately 30% or more. Using administrative data containing the earnings histories of parents and children, the IGE is estimated to be around 0.6. This suggests that the United States is substantially less mobile than previous research indicated. Estimates of intergenerational mobility are significantly lower for families with little or no wealth, offering empirical support for theoretical models that predict differences due to borrowing constraints.