© 2015 by the American Academy of Neurology. Neurodevelopmental disorders are a group of heterogeneous conditions characterized by a delay or disturbance in the acquisition of skills in a variety of developmental domains, including motor, social, language, and cognition. This article reviews the most commonly diagnosed neurodevelopmental disorders, which include attention deficit hyperactivity disorder (ADHD), autism spectrum disorder, global developmental delay, and intellectual disability and also provides updates on diagnosis, neurobiology, treatment, and issues surrounding the transition to adulthood. Recent Findings: Although symptoms emerge at discrete points in childhood, these disorders result from abnormal brain maturation that likely precedes clinical impairment. As a result, research has focused on the identification of predictive biological and behavioral markers, with the ultimate goal of initiating treatments that may either alter developmental trajectories or lessen clinical severity. Advances in the methods used to identify genetic variants, from chromosomal microarray analysis to whole exome sequencing, have facilitated the characterization of many genetic mutations and syndromes that share common pathways to abnormal circuit formation and brain development. Not only do genetic discoveries enrich our understanding of mechanisms underlying atypical development, but they also allow us to identify more homogeneous subgroups within this spectrum of conditions. Impairments do continue into adulthood, with challenges in the transition to adulthood including the management of comorbidities and the provision of educational and vocational supports. Summary: Advances in our understanding of the neurobiology and developmental trajectories of these disorders will pave the way for tremendous advances in treatment. Mechanism-based therapies for genetic syndromes are being studied with the goal of expanding targeted treatments to nonsyndromic forms of neurodevelopmental disorders.