There are very few empirically-supported interventions available for infant siblings of children with Autism Spectrum Disorders (Sibs-ASD) whom genetic studies reveal are at risk for a variety of developmental challenges, with a significantly increased risk for ASD and other social, cognitive, and language difficulties. This project will pilot a novel behavioral intervention, the Infant-Toddler Years Pivotal Response Treatment (ITY-PRT), designed to enhance the frequency of communication and social engagement in for infant siblings of children with who demonstrate developmental delays at 12-15 months of age. This project will assess the feasibility and efficacy of this early intervention in preparation for larger clinical trials of efficacy. Utilizing a randomized-controlled group design, 30 infant SIBS-ASD who demonstrate significant delays in communication and/or social interaction at 12-15 months of age will be randomly assigned to, over the course of 6 months, receive either ITY-PRT in addition to a standard referral to community treatment. The frequency of child communication, child social interaction behaviors, and parental bids for communication during parent-child interaction probes, as well as changes in standardized measures of development and social behavior will be studied to assess efficacy of this intervention.