As the first in a trio of pieces devoted to incorporating immigration into policy models, this review of research on immigrant earnings trajectories brings to light several findings. Controlling for demographic and human capital characteristics, immigrants often start their U.S. lives at substantially lower earnings, but experience faster earnings growth than natives with comparable years of education and experience. The extent to which the earnings trajectories of immigrants and natives differ varies by country of origin, with the source-country's level of economic development being a key determinant of the size of the U.S.-born/ foreign-born difference. The earnings profiles of immigrants from economically developed countries such as Japan, Canada, or Western Europe resemble those of U.S. natives who are of the same age and education level. In contrast, the earnings of immigrants from developing nations tend to start well below those of U.S. natives with comparable education levels and experience, but rise more rapidly than their U.S. counterparts. Comparing the earnings profiles of immigrants of similar age, sex, and years of schooling, over time and across groups, a strong inverse relationship emerges between their initial earnings and their subsequent U.S. earnings growth. In other words, the lower (higher) the initial earnings are, the higher (lower) the earnings growth. These and other research results have important implications for the projection of immigrant earnings and emigration in microsimulation models, as discussed in the two articles following this one: (1) "Adding Immigrants to Microsimulation Models" and (2) "Incorporating Immigrant Flows into Microsimulation Models".