The human brain undergoes great changes from birth to adult age. Insight into this complex process has been tremendously enhanced over the last two decades by imaging studies of the brain. Such studies have documented sustained changes in the cerebral cortex, subcortical structures, and white matter of the brain. Longitudinal studies with several time-points are, however, needed to track the trajectories of structural and functional changes in the brain’s tissues and connections. This will enable us to study how these vary across different brain regions and between individuals.