The Japan Clinical Oncology Group Head and Neck Cancer Study Group (JCOG-HNCSG), established in 2011, is the leading academic cooperative group for head and neck cancer clinical research in Japan. Since its formation in 2005, the group has conducted multiple prospective studies aimed at improving outcomes and quality of life for patients with head and neck cancer. Among its landmark achievements, JCOG1008 demonstrated the non-inferiority of weekly cisplatin compared with three-weekly cisplatin in postoperative chemoradiotherapy and established a new treatment option for high-risk patients (J Clin Oncol. 2022). More recently, the primary results of JCOG1912, a randomized trial evaluating dose reduction in elective nodal irradiation, were presented at ESMO 2025. In addition, the T4b cohort results of JCOG1212, investigating RADPLAT for locally advanced maxillary sinus cancer, have been accepted for publication in ESMO Open following the previously reported favorable outcomes in the T4a cohort. JCOG-HNCSG is currently conducting two prospective studies: JCOG2405, a randomized phase III trial of weekly cisplatin-based chemoradiotherapy versus radiotherapy alone in elderly patients unfit for high-dose cisplatin, and JCOG2407, evaluating omission of elective neck dissection in T3–T4aN0 laryngeal cancer. In addition, a new randomized phase III trial investigating salvage systemic therapy strategies for recurrent or metastatic head and neck cancer is under development. The group also promotes patient-reported outcomes, quality-of-life research, translational studies, and international collaboration. Through active participation in HNCIG-led projects, JCOG-HNCSG has expanded its global presence. In the ongoing HNCIG/IFHNOS CUP study, JCOG has achieved the second-highest patient accrual after the United Kingdom. JCOG-HNCSG remains committed to advancing evidence-based multidisciplinary care for patients with head and neck cancer.