Neuroimaging was revolutionized by the development of computed tomography (CT) and standard T1- and T2-weighted magnetic resonance imaging (MRI). Magnetic resonance imaging and CT can adequately distinguish hemorrhage from infarction and depict ischemic stroke 12 to 24 hours after onset. However, during the critical initial hours after the onset of ischemic stroke, these imaging technologies do not adequately demonstrate the location and extent of infarction. Diffusion-weighted MRI and perfusion imaging, as well as advances in magnetic resonance spectroscopy, will enhance our ability to evaluate ischemic stroke shortly after onset. Some of the uses of MRI techniques are as follows: (1) Diffusion-weighted imaging can depict the location and extent of the ischemic lesion as soon as a stroke patient is available for examination. (2) Perfusion imaging evaluates blood flow within the brain's microvasculature and can reveal regions of perfusion deficits corresponding to major vascular territories. (3) Magnetic resonance spectroscopy evaluates metabolic abnormalties associated with focal brain ischemia by specific biochemical measurements. These MRI techniques will rapidly provide important information to clinicians about ischemia, guiding diagnosis and helping in the development of acute stroke interventions to improve outcome.