Since its start as the Eastern Cooperative Cancer Chemotherapy Group in 1955, the Eastern Cooperative Oncology Group (ECOG) has been at the vanguard of adult cancer clinical research in the United States, and for more than 50 years its research findings have influenced cancer care worldwide. While the cancer clinical research milieu has changed considerably since its inception, the ECOG, through sound leadership and a committed membership, has maintained its pioneering roles in scientific discovery and defining standards of cancer care for all adult cancers.