This paper uses a nets data source to investigate differences in occupational achievement among a large number of ethnic groups. The November, 1979 Current Population Survey is a unique source since it provides information on both the ancestry and nativity of a large national sample of respondents. These data are particularly valuable because they permit the identification of first-, second- and third- or higher-generation individuals, thereby providing a clearer picture of the process of assimilation. We focus upon the achievements of men, age 20 to 64, classified simultaneously by nativity and ethnicity. Not surprisingly, there are notable differences in the occupational attainment of foreign-born men. Some of these differences are due to the diverse social and economic backgrounds of the different nationalities, but important differences in the rates of return to background characteristics are also evident. The assimilation perspective predicts that eventually ethnic background will no longer be an important determinant of socioeconomic achievement. By the third generation, we find this to be true for the most part, although important exceptions are discussed in this paper.