Biologic connectionism holds as its central tenet that the cognitive, behavioral, and motor functions of the brain are derived from the complex interconnections of simple neural processing units. Much can be learned about the human mind through the study of the brain's connections in normal and diseased states. This article summarizes the essential features of the tensor model of diffusion, outlines newer approaches to overcoming the limitations of the tensor, and provides normal and clinical examples of white matter anatomy derived using diffusion tensor imaging and more sophisticated high angular resolution diffusion imaging methods. Diffusion MR imaging is a powerful adjunct to techniques for studying brain function.