Diffusion-weighted Imaging (DWI) is a advantageous method for early detection of cerebral ischemia. DWI with echo-planar sequence (EP-DWI) offers multisectional images sensitive to cytotoxic edema in a very short aquisition time and is almost free from motion artifact. However, the susceptibility artifacts and low spatial resolution of EP-DWI must be improved. In estimation of DWI, influence of T2 must be considered, because DWI is almost always based on T2-weighted imaging. DWI is applied to other cerebral disorders such as degenerative and demyelinating disease, infectious disease, tumors or so. In order to demonstrate water diffusion precisely, diffusion tensor imaging (DTI) must be introduced and applied to anisotropy indices such as fractional anisotropy (FA) and depiction of neurofiber direction, tractography. Measurements of FA in various degenerative diseases may contribute to differentiation in normal appearing white matter. Diffusion tensor tractography may provide more information about relationship of major white matter tract such as corticospinal tract with brain lesion. Furthermore, DWI and DTI are expected to demonstrate diffusion of protons of aminoacids such as choline, creatine, NAA and provide more pertinent information of regional pathologic state of the brain in future.