Submitted article deals with the problem of over-education. It offers a brief overview of existing explanations. It introduces a method of over-education measurement based on internationally used classifications ISCO and ISCED. The article brings also some evidence on over-education measured by this method. The analysis is focused on over-education of workers with a degree, which becomes especially interesting in the light of the tertiary education expansion. The question is, in what sense does over-education refer to the supply-demand relations on the labour market. International comparisons of over-education in European countries give some partial answers.