Neurosurgery must always carefully balance the benefit of surgical therapy against the risk of causing or increasing neurological symptoms. Preoperative risk assessment on the basis of standard anatomical imaging alone is often insufficient because of inherent variations in motor representation from one patient to the next and because pathology can obscure or alter the anatomy. Several sophisticated new technologies have been developed in the past 30 years: PET, fMRI, MEG, TMS, DTI, which substantially improve the capabilities of the neurosurgical team to assess cortical function and improve their surgical planning. Neurosurgeons need to understand and use this modern technology to create patient-specific cortical maps and management plans, in order to improve therapeutic effectiveness and reduce morbidity. This chapter presents the current technologies in use for preoperative mapping of the motor system.