Abstract Language delay and impairments are common in autism spectrum disorders (ASDs), as are sensory (including auditory) anomalies. Since acquisition of spoken language relies on the integrity of the auditory system, language delay and impairments may be related to sound processing abnormalities that are frequently observed in children with ASDs (despite normal peripheral hearing). However, it is not understood if and how early auditory brain anomalies may developmentally contribute to impaired language development. This project will examine the maturation of auditory and language systems in the brain across early childhood, during the critical period for language acquisition. We will employ a longitudinal design and multimodal neuroimaging, including high-resolution anatomical, diffusion, and functional magnetic resonance imaging (MRI), with added frequent and extensive behavioral and neuropsychological assessments. Our central hypothesis is that early disruptions to cortical sound processing precede and predict language impairments in ASDs and may thus be considered causal contributors ? a hypothesis that has been frequently considered in the literature, but never tested at the neural level. Our aims are to thoroughly characterize the structural integrity and functional differentiation of the cortical auditory and language systems (Aim 1) and their maturational trajectories (Aim 2) in toddlers with ASDs and age-matched typically developing peers. This will allow us to establish whether neural abnormalities in cortical processing of complex sounds in toddlers are predictive of language development and social behavior at the pre-school age (Aim 3). The rationale and translational significance of this project are that identification of alterations in brain development linked to language delay and impairment in the first years of life will allow for more targeted interventions in the auditory domain at a time when they are most effective.