Prior research has found that immigrants are often overeducated: their educational attainment is higher than required or commonly observed in their occupation. Yet, less is known about the education–occupation mismatch among immigrants’ children and grandchildren (the second and third generations). Using the French Trajectories and Origins 2 (TeO2, 2019–2020) survey, we test theoretically grounded hypotheses on the level of vertical (educational attainment) and horizontal (field of study) mismatch in the first, second, and third generations as well as on the mechanisms underlying the mismatch. Results indicate that vertical mismatch is substantially lower in the second and third generations than in the first, supporting the hypothesis that vertical mismatch is largely the result of imperfect international transferability of credentials. By contrast, higher levels of horizontal mismatch persist in the second and third generations among men of non-European descent. Differences in horizontal mismatch between immigrants’ and natives’ descendants are largely accounted for by initial sorting into fields of study.