This article focuses upon the phenomenon of over-education in Italy, proposing an original measure which is based on cross-dataset comparison between the actual occupation and the educational level of workers for each ISCO 4 digit class. The level of analytical detail and the crossed use of a self-declared and a statistical method for defining over-education allow achieving an accurate and punctual measure of over-education of labour force. By over-education we mean here the proportion of workers employed in occupational positions in which their educational level is higher than requested. Building on this measure, the article identifies the main factors associated with over-education, considering aspects connected with labour supply (i.e. characteristics of workers), labour demand (i.e. economic sector or size of firms), and the contract arrangement. The descriptive analysis shows that over-education is concentrated especially among young workers, carrying the possible risk of impeding the human capital exploitation achieved during the education. However, a logistic regression model shows that the relation between age and over-education - which is still significant - is far from being linear, while further factors are associated to the phenomenon. In particular, factors related to labour demands expose sensibly to the risk of over-education: Italian productive structure is not specifically oriented towards knowledge-intensive economical activities, thus not offering suitable preconditions for public or private investments in human capital. Secondly, the type of labour contract contributes to increase the risk of over-education, above all for temporary and part-time contracts (characterised by a weaker subordination position). In sum, the analysis suggests the existence of a widespread and complex mismatch between education and labour market in Italy.