The European Commission’s Directorate-General for Internal Market, Industry, Entrepreneurship and SMEs (DG GROW), with the scientific support by the European Commission Joint Research Centre (JRC), assesses the Performance of Small and Medium Enterprises in Europe, depending on the performance in the ten principles of: (1) Entrepreneurship, (2) ‘Second chance’, (3) ‘Think small first’, (4) ‘Responsive administration’, (5) State aid & public procurement, (6) Access to finance, (7) Single market, (8) Skills and innovation, (9) Environment, and (10) Internationalisation. This JRC technical report describes the underlying rationale behind the quantitative measurement of these principles and discusses the methodological approach which has been followed to calculate how countries perform in the outlined principles, from the choice of the indicators, to the data quality controls (including missing data and outliers), normalization and weightings, to the statistical coherence and robustness checks.