My main interest in this thesis is to estimate the returns of education and determine if there are differences in the returns to education between men and women considering educational mismatch variables. Then, I study the role they have determining the gender wage gap using a Oaxaca-Blinder Decomposition. In aggregate, this work studies gender differences in wages driven by differences in levels and returns to educational mismatch, but also occupation, experience, marital status, children, sector and other variables considering two samples: a whole representative sample of the U.S. labor force and a graduate sample, following by studying their relative weights in the wage gap.