Human brain networks based on neuroimaging data have already proven useful in characterising both normal and abnormal brain structure and function. However, many brain disorders are neurodevelopmental in origin, highlighting the need to go beyond characterizing brain organization in terms of static networks. Here we review the fast-growing literature shedding light on developmental changes in network phenotypes. We begin with an overview of recent large-scale efforts to map healthy brain development, and we describe the key role played by longitudinal data including repeated measurements over a long period of follow-up. We also discuss the subtle ways in which healthy brain network development can inform our understanding of disorders, including work bridging the gap between macroscopic neuroimaging results and the microscopic level. Finally, we turn to studies of three specific neurodevelopmental disorders which first manifest primarily in childhood and adolescence/early adulthood, namely psychotic disorders, attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). In each case we discuss recent progress in understanding the atypical features of brain network development associated with the disorder and we conclude the review with some suggestions for future directions.