In this paper we develop and test a new set of measures of skill mismatches, based on data on skill levels and skill use in the domains of literacy and numeracy from the PIAAC project. The measures we develop represent the extent of skill use relative to one’s own skill level. We test the measures by examining their relation to a number of labour market outcomes. We subsequently examine how mismatches are distributed across and within a large number of countries, and use our results to reflect on possible causes and consequences of mismatches. We find that, in general, higher skill utilization is always beneficial in terms of productivity and job satisfaction, and that "overutilization" of skills therefore points more towards a fuller use o...