Recent empirical studies of the effects of immigration have tended to focus on short-run outcomes. This column considers the longer run by examining how mass migration at the turn of the 20th century has affected US outcomes today. Higher historical immigration between 1860 and 1920 is found to result in significantly better social and economic outcomes today. The results suggest that the long-run benefits of immigration can be large, can persist across time, and need not come at a high social cost.