PROJECT SUMMARY/ABSTRACT Down Syndrome (DS) impacts approximately 1 in about 700 babies born in the United States. Language and motor development in DS are significantly delayed in early childhood; however, little research has investigated how language and motor skills interact and support each other. In response to the NIH INCLUDE Down Syndrome Research Plan, the proposed study will address several gaps in our understanding of DS. First, we will implement multiple methods, including technology, to measure language and motor development across direct assessments, naturalistic measurements, parent reports, and free play observations. Second, we intend to actively recruit and enroll over 60% of participants from racially/ethnically minoritized backgrounds. Finally, we will collect longitudinal data to track measures that may be sensitive to developmental change. Using multiple methods, we will track developmental trajectories of language and motor skills in infants with Down Syndrome (DS) and typically developing infants over a 12-month period. The goal is to measure language, communication, motor skills, and physical activity to better understand how these skills develop and interact with each other over time. If funded, we will recruit 36 infants with DS (age 6 months – 18 months) and 36 typically developing (TD) infants (age 6 months – 18 months) and follow them for 12 months. We intend to recruit at least 60% of our sample from racial/ethnic minority backgrounds (i.e., Hispanic/Latino, Black/African American, Asian, Native American). Infants and their caregivers will complete standardized questionnaires and assessments at study entry, then two more times, 6 months apart, for a total of three assessments in a 12- month period of time. This research will provide critical data on the early development of racially/ethnically diverse infants with DS to inform intervention strategies and supports.