White matter injury and abnormal maturation are thought to be major contributors to the neurodevelopmental disabilities observed in children and adolescents who were born preterm. Early detection of abnormal white matter maturation is important in the design of preventive, protective, and rehabilitative strategies for the management of the preterm infant. Diffusion Tensor Imaging (DTI) allows non-invasive, in vivo visualization and quantification of white matter tracts and has become a valuable tool in assessing white matter maturation in children born preterm. We will review the use of DTI to study white matter maturation and injury in the preterm brain.