The North Central Cancer Treatment Group (NCCTG) was founded in 1977 as a regional cooperative group to allow cancer patients in the upper Midwest of the United States to gain access to clinical trials in oncology by establishing a network of community oncology practices with one academic research base, the Mayo Clinic. Since then, the NCCTG has grown into an international cooperative group with 43 members in 33 US states and Canada. This article details 30 years of achievements of the NCCTG, including important scientific contributions from disease-specific and treatment modality committees, the cancer control program, patient-reported outcomes and quality-of-life research, and biostatisticians that support the NCCTG's specific aims: to improve the duration and quality of life of cancer patients, to enhance our understanding of the biological consequences of cancer and its treatment, and to improve methods for clinical trial conduct.