A greater extent of resection of the contrast-enhancing (CE) tumor part has been associated with improved outcomes in high-grade glioma patients. Recent results suggest that resection of the non-contrast-enhancing (NCE) part might yield even better survival outcomes (supramaximal resection, SMR). Therefore, this study evaluates the efficacy and safety of SMR with and without mapping techniques in HGG patients in terms of survival, functional, neurological, cognitive, and quality of life outcomes. Furthermore, it evaluates which patients benefit the most from SMR, and how they could be identified preoperatively. This study is an international, multicenter, prospective, 2-arm cohort study of observational nature. Consecutive HGG patients will be operated with supramaximal resection or maximal resection at a 1:3 ratio. Primary endpoints are: 1) overall survival and 2) proportion of patients with NIHSS (National Institute of Health Stroke Scale) deterioration at 6 weeks, 3 months, and 6 months postoperatively. Secondary endpoints are 1) residual CE and NCE tumor volume on postoperative T1-contrast and FLAIR MRI scans 2) progression-free survival; 3) onco-functional outcome, and 4) quality of life at 6 weeks, 3 months, and 6 months postoperatively. The study will be carried out by the centers affiliated with the European and North American Consortium and Registry for Intraoperative Mapping (ENCRAM).