This paper examines the quality of jobs generated during periods of job expansion from the 1960s through to the 1990s in the USA. The central results of the study are: first, the long 1990s economic boom produced a pattern of asymmetrically polarized job expansion: very strong expansion of jobs in the top tier of the employment structure combined with very limited growth in the middle. Secondly, while job growth at the top was strong in the 1990s, the overall pattern of job expansion was much less favorable for the labor force as a whole than in earlier expansions. Thirdly, there has been a dramatic change in the racial and gender patterns of job expansion since the 1960s: gender differences in job expansion were very sharp in the 1960s and quite muted in the 1990s, while the racially polarized character of job expansion has increased, especially at the bottom of the employment structure. Finally, immigration, especially of Hispanics, is deeply connected to the employment expansion in the bottom tiers of the employment structure. Underlying these descriptive patterns are dramatic changes in the sectoral patterns of job expansion in the 1990s compared with the 1960s: the much slower growth of middle-level jobs in the 1990s is rooted in the decline of manufacturing; the stronger growth of bottom-end jobs is rooted in accelerated growth of retail trade and personal services in the 1990s; and the very strong growth of high-end jobs is rooted in high tech sectors.