This paper aims to explain both related and different concepts of educational and skill mismatches. In the first part a clear distinction between skill and educational mismatch is made and advantages and disadvantages of using each approach are listed. An overview of meanings and characteristics of different types of mismatch is provided as well. This part of the paper deals also with potential causes of mismatches in the labour market as well as consequences of mismatches. Next section offers the information on measures of educational and skill mismatches and a new approach for measuring skill mismatch is introduced. Due to recently Publisher results from PIAAC survey containing measures of skills and also information about qualifications, educational as well as skill mismatches can be investigated and several methods of their measurement can be compared. The comparison is drawn in relation to the distribution of mismatches among different demographic groups.