The EORTC Breast Cancer Group (BCG), created in 1962, is a multidisciplinary group involving surgeons, medical oncologists, radiation oncologists, pathologists, basic scientists, and clinical research fellows. Currently, more than 80 member's institutions across Europe are participating in the group studies. The main goal of the BCG is to conduct high-quality international clinical trials covering all areas of breast cancer care: from loco-regional to systemic disease control, and from in situ carcinoma to metastatic disease. Over 50 years, the BCG has performed dozens of clinical studies including several thousands of patients. Many practice-changing trials and major achievements were conducted optimizing local control, improving systemic therapy in early and metastatic breast cancer, pioneering work in clinical-translational trials and collaboration within intergroup trials. The strategic plan of the BCG for future research includes three distinct albeit overlapping areas: loco-regional therapy, (neo-)adjuvant systemic therapy, trials in the metastatic setting, and niche population studies. For each of these areas the group has considered the prevailing EORTC strategy of focusing on practice-changing studies and translational research, with an emphasis on niche trials. During five decades, the BCG has successfully performed a series of practice-changing trials enrolling several thousands of patients. These studies have contributed to the clinical knowledge on the treatment of breast cancer and have influenced clinical practice and breast cancer patients' outcome worldwide.