The axonal membrane and the myelin sheets around axons restrict water diffusion perpendicular to the fiber orientation in white matter but not along the axon’s main axis, which leads to anisotropic diffusion of water. Over the last decade, the quantitative measurement of this anisotropy by using what has been called diffusion tensor imaging (DTI) has become well established in research applications, revealing the macroscopic threedimensional architecture of white matter and the constituent white matter tracts. The depiction of white matter architecture in orientation-based color coding is a visualization approach in which the image brightness depicts diffusion anisotropy and a red/green/blue color scheme indicates tract orientation. Using a multiple region-of-interest (ROI) approach that exploits existing anatomic knowledge of tract trajectories, white matter bundles of interest can be reconstructed non-invasively in vivo. We have created a human white matter brain atlas, consisting of projection, association, and commissural fibers as well as brainstem fibers, examples of which are depicted here.