Diffusion-weighted MRI provides image contrast that is dependent on the molecular motion of water. Diffusion-weighted imaging is the most reliable method for early detection of cerebral ischemia, for the definition of infarct core, and for the differentiation of acute ischemia from other disease processes that mimic stroke. Diffusion tensor imaging and diffusion kurtosis imaging may offer additional diagnostic information on the microstructural status of tissue. This review discusses the development and applications of diffusion-weighted imaging, diffusion tensor imaging, and diffusion kurtosis imaging in acute and chronic ischemia.