Workers with the same level of formal education receive different wages and, additionally, wage differentials between workers can be observed at the same job. To investigate these events in the Spanish labor market, this piece of research focuses on the influence of education and qualification mismatches on individual wages. To address the issue, a number of hypotheses are proposed. i) The mismatch between levels of education required by jobs and those possessed by workers are key determinants of wage differential between workers with the same level of formal education. ii) The rate of return to one year additional schooling depends both on the required education in a job and on the education possessed by the supply of labor. iii) Workers with similar characteristics receive different wages according to whether they have or not the qualification required in their job. We use data from the Spanish Household Panel Survey corresponding to years 1994-1998. To explore the education match, the definition of the required level of education is based on the modal level within 2-digit ISCO88 occupational classification; the definition match in qualifications is based on workers' self-assessments. To test the research hypotheses we use diverse specifications of wage functions. Preliminary results show that: Hypothesis i: In general, overeducated (undereducated) workers earn significantly lower (higher) wages than those whose have the same formal education and are accurately match in their jobs. Hypothesis ii: The rate of return to one year overeducation is positive but smaller than the return to one year required education, whereas the rate of return to one year undereducation is negative. Hypothesis iii: Both overqualified and underqualified workers earn lower wages than those who are adequately matched in their job. REFERENCES Alba-Ramírez, A. & Blázquez, M. (2004): Types of job match, overeducation and labour mobility in Spain. En Büchel, F., Grip, A. y Mertens, A (Eds.) Overeducation in Europe: current issues in theory and policy. Edward Elgar, Cheltenham. Dolton, P. & Vignoles, A. (2000): The incidence and effects of overeducation in the U.K. graduate labour market. Economics of Education Review, vol. 19, 179-198. Duncan, G. & Hoffman, S.D. (1981): The incidence and wage effects of overeducation. Economics of Education Review, vol. 1, 75-86. Cohn, E. & Khan, S.P. (1995): The wage effects of overschooling revisited. Labour Economics, vol. 2, 67-76. Cohn, E. & Ng. Y. C. (2000): Incidence and wage effects of overschooling and underschooling in Hong Kong. Economics of Education Review, vol. 19, 159-168. Frenette, M. (2004): The overqualified Canadian graduate: the role of the academic program in the incidence, persistence, and economic return to overqualification. Economics of Education Review, vol. 23, 29-45. Sicherman, N. (1991): "Overeducation" in the labor market. Journal of Labor Economics, vol. 9, no. 2, 101-122. Verdugo, R. & Verdugo, N.T. (1989): The impact of surplus schooling on earnings: some additional findings. Journal of Human Resources, 21, 629-643.