The astonishing hypothesis of neuroscience is that thoughts and emotions are the interactions of neuronal signals. The synapses that mediate interactions between cortical neurons are located within a thin layer of cells that covers the surface of the brain. The local results of these interactions in the gray matter are communicated to distant brain regions along pathways comprising many axons. Mapping these pathways- the white matter tracts- is an essential part of understanding brain function. Until recently, there have been no non-invasive methods to estimate white matter tracts in the living human brain. New magnetic resonance and computational methods have emerged that provide a great deal of information about these structures in healthy and diseased brains. These Diffusion Tensor Imaging (DTI) methods measure water diffusion throughout the brain. These measurements provide an aggregate measure of the microscopic structure of living brain tissue that has sparked the development of statistical algorithms to compare the local diffusion properties in different brains, such as those of healthy and diseased groups. Further, a number of labs have developed Fiber Tractography (FT) algorithms that use the diffusion measurements to estimate the pathways followed by the white matter fiber tracts as they course their way from one gray matter region to another. In this tutorial, we will describe (a) the measurements, (b) the statistical algorithms, (c) the FT algorithms, and (d) various applications.