Diffusion tensor imaging (DTI) offers researchers and clinicians a new noninvasive window into the developing human brain. DTI improves on conventional MR imaging, such as T1- and T2-weighted sequences, through its sensitivity to many microstructural features of neural organization. This has enabled visualization of the early cerebral laminar architecture in premature infants, of developing white matter prior to myelination, and of the microarchitecture of the cerebral cortex during preterm maturation. Furthermore, three-dimensional fiber tractography based on DTI can reveal the developing axonal connectivity of the human brain, as well as aberrant connectivity in structural brain malformations. The new insights into brain maturation afforded by DTI promise to improve the diagnostic evaluation of an array of neurodevelopmental disorders.