In humans, the period from term birth to ~2 years of age is characterized by rapid and dynamic brain development and plays an important role in cognitive development and risk for disorders such as autism and schizophrenia. Recent imaging studies have begun to delineate the growth trajectories of brain structure and function in the first years after birth and their relationship to cognition and risk for neuropsychiatric disorders. This Review discusses the development of grey and white matter, structural and functional networks, as well as genetic and environmental influences on early childhood brain development. We also discuss initial evidence regarding the usefulness of early imaging biomarkers for predicting cognitive outcomes and risk for neuropsychiatric disorders.