Early parent-infant interaction is a foundation for infant development. Further, transactional processes involving parent infant interaction may play a role in the development of clinical conditions such as Autism Spectrum Disorder (ASD). Traditional approaches for studying parent child interaction involve manual coding of video recordings, which is extremely time consuming and has limited precision in terms of fine-grained analysis of a key aspect of the interaction: looking patterns. Here, I propose a novel approach to studying early dyadic interaction, by the use of dual live eye tracking. This non-invasive method can be used to record eye movements of both infant and parent simultaneously, as they interact with each other. I will thus be able to, for the first time, provide a detailed characterization of gaze patterns during parent infant interaction, as well as to determine how these patterns relate to characteristics of both infant and parent. By taking a longitudinal approach, I will also be able to investigate how interactional gaze patterns evolve over time. Specifically, I will evaluate the recent hypothesis that infants actively shape their own social environment (parental behaviors) through their early looking patterns. Finally, by including both typically developing infants and infants at high risk for ASD, putative associations with later atypical development will be directly assessed.