The Breast International Group (BIG) is a non-profit organisation for academic breast cancer research groups from around the world, with its headquarters in Brussels, Belgium. BIG facilitates and accelerates breast cancer research at the international level by stimulating cooperation between its members and other academic networks, and collaborating with, but working independently from, the pharmaceutical industry. Large-scale cooperation is crucial to make significant advances in breast cancer research, reduce unnecessary duplication of effort, and optimally serve those affected by the disease.