Although language impairment is common is ASD, it is unclear at what point language acquisition in individuals with ASD begins to diverge from the typical trajectory. Recent developmental studies of ASD suggest that impairment in language and other domains may be present by 12 months (Mitchell, et al., 2006), but behavioral measures have failed to find consistent deficits before this age. Neurophysiological measures, which can be more sensitive to dysfunction before 12 months, have not yet been used to study very early language processing in ASD. The current project will study auditory ERP longitudinally in infants at risk for developing ASD (HRA) or language impairment (HRL) along with low risk controls (LRC). Our preliminary work suggests that HRA infants fail to develop lateralized ERP response to speech stimuli at 9 and 12 months. Here, we will examine whether this atypical asymmetry persists over the second and third years of life and whether it is predictive of later symptoms of ASD or SLI. Additionally, we will use ERP to examine phonemic perceptual narrowing between 6 and 12 months to determine whether this is delayed in infants who are later diagnosed with ASD and whether it is predictive of later language ability in HRA infants as it is in typical development. Finally, we will examine whether atypical ERP response to speech between 6 and 12 months may act as a neurobiological risk marker for ASD diagnosis, helping us to detect ASD over the first year of life.