The brain is highly susceptible to injury from any process that deprives its cells of oxygen, glucose, and other essential nutrients, and is therefore critically dependent on blood flow or perfusion. With hypoperfusion or ischemia, blood flow to the brain may be diminished to a level incompatible with normal function, eventually leading to acute ischemic stroke. Magnetic resonance (MR) imaging is one of several imaging methods used to evaluate brain perfusion and stroke. Using a multisequence approach comprised of conventional spin echo, inversion recovery, and heme-sensitive gradient echo pulse sequences, MR angiography, and diffusion and perfusion sensitive techniques, MR imaging is capable of identifying vascular lesions, measuring abnormal blood flow, and depicting the metabolic and structural consequences of ischemia. MR imaging objectives and strategies for the diagnosis of acute ischemic stroke in humans and animals, terminology, pathophysiology, and normal vascular anatomy are reviewed.