Chapter 6. Immigrants and Immigrant Health Using the National Health Interview Survey (1989–2011) we document the Healthy Immigrant Effect (HIE)—immigrants are in better health upon arrival in the United States than their native counterparts but this health advantage erodes over time—irrespective of the health measure race ethnicity or gender. Further most immigrant groups arrive lighter than natives and then converge towards their native counterparts suggesting acculturation plays a role in explaining the HIE. Finally we show that constraining the period effects to be the same for natives and immigrants may lead one to conclude there is no evidence of unhealthy assimilation particularly if the rates at which natives and immigrants are becoming unhealthy differ from each other and change across time periods.