Although diffusion-weighted imaging (DWI) of the brain has gained widespread clinical acceptance, DWI of the spine and spinal cord is less well known. This article briefly reviews some of the principles and concepts of diffusion imaging, including technical considerations with regard to in vivo DWI of the spine and spinal cord, and summarizes the research and clinical experience to date. With further development and refinement, DWI eventually may provide useful and important insight into a variety of diseases of the spine and spinal cord.