Resection of glioblastoma in or near functional brain tissue is challenging because of the proximity of important structures to the tumor site. To pursue maximal resection in a safe manner, mapping methods have been developed to test for motor and language function during the operation. Previous evidence suggests that these techniques are beneficial for maximum safe resection in newly diagnosed grade 2-4 astrocytoma, grade 2-3 oligodendroglioma, and recently, glioblastoma. However, their effects in recurrent glioblastoma are still poorly understood. The aim of this study, therefore, is to compare the effects of awake mapping and asleep mapping with no mapping in resections for recurrent glioblastoma. This study is an international, multicenter, prospective 3-arm cohort study of observational nature. Recurrent glioblastoma patients will be operated with mapping or no mapping techniques with a 1:1 ratio. Primary endpoints are: 1) proportion of patients with NIHSS (National Institute of Health Stroke Scale) deterioration at 6 weeks, 3 months, and 6 months after surgery and 2) residual tumor volume of the contrast-enhancing and non-contrast-enhancing part as assessed by a neuroradiologist on postoperative contrast MRI scans. Secondary endpoints are: 1) overall survival (OS), 2) progression-free survival (PFS), 4) health-related quality of life (HRQoL) at 6 weeks, 3 months, and 6 months after surgery, and 4) frequency and severity of Serious Adverse Events (SAEs) in each arm. Estimated total duration of the study is 5 years. Patient inclusion is 4 years, follow-up is 1 year. The study will be carried out by the centers affiliated with the European and North American Consortium and Registry for Intraoperative Mapping (ENCRAM).