Echo-planar imaging is a fast magnetic resonance (MR) imaging technique that allows acquisition of single images in as little as 20 msec and performance of multiple-image studies in as little as 20 seconds. Echo-planar imaging achieves its speed by obtaining all spatial-encoding information after a single radio-frequency (RF) excitation. Conventional imaging requires multiple-RF excitations, separated by the repetition time (TR), to acquire this information. An "infinite" TR, routine lipid suppression, and sensitivity to magnetic susceptibility are other features of echo-planar imaging. Standard pulse sequences are used to obtain echo-planar images, which have diagnostic utility similar to that of conventional MR images. Echo-planar imaging is less sensitive to motion than is conventional MR imaging and allows imaging of rapidly changing physiologic processes such as blood flow and kinetic activity. Echo-planar imaging is opening new areas of MR imaging research and clinical applications.