This article focuses on the influence of social background on overeducation in Spain, understanding family socialisation as a source of knowledge and skills gain. The dramatic education expansion experienced in Spain in combination with a high percentage of low-skilled jobs has promoted overeducation occurrence to a larger extent than in other Organisation for Economic Cooperation and Development (OECD) countries. Using the Survey of Adult Skills (PIAAC) data results suggest that overeducation affects at least over a quarter of the working population. Younger and middle aged workers are more likely to be overeducated compared to the senior ones, while women are more prone to be overeducated than men. Workers whose mothers have higher education are less likely to be overeducated compared to those whose mothers have basic education, while fathers’ education is practically irrelevant to predict workers’ overeducation. Thus, a mother’s education is the most relevant social background indicator to predict overeducation, even when controlling for firm characteristics and skills level.