International Consortium on Mammographic Density: Methodology and population diversity captured across 22 countries

•The International Consortium on Mammographic Density (ICMD) is a pooling study of individual-level epidemiologic data and mammographic density information.•The rationale and methods of ICMD are described.•11755 women, from 27 studies in 22 countries are included.•The immense heterogeneity in breast cancer risk factors are highlighted.