The resection of brain tumors is limited by the surgeon's ability to precisely define margins. To overcome this problem, various neuro-navigational tools have been used. The development of image-guided navigation systems represents a substantial improvement in the microsurgical treatment of various intracranial lesions. However, a major drawback of this technology is that they use images acquired preoperatively, on which the surgical planning and intraoperative performance is based. As the intracranial anatomy dynamically changes during a neurosurgical procedure, only intraoperatively acquired images can provide the neurosurgeon with the information needed to perform real-time, image-guided surgery. Because magnetic resonance imaging best delineates the soft-tissue extent of most tumors, it currently remains the superior method for intraoperative image guidance. In this review, we outline the development as well as current and possible future applications of the intraoperative MRI (iMRI) unit at the Brigham and Women's Hospital, Boston, MA.