The OECD Development Centre’s Social Institutions and Gender Index (SIGI) is an innovative measure of discriminatory social institutions. The SIGI’s indicators address the de jure and de facto situations of discriminatory social institutions across five sub-indices: discriminatory family code, restricted physical integrity, son bias, restricted resources and assets and restricted civil liberties. A methodological framework was established to best seize the complex relationship between gender equality and discriminatory social norms. This background paper aims to explain how the composite index and its sub-indices are constructed.