This report summarizes research about development during the first 3 years of life. It highlights research in domains that are foundational for later school readiness and success, including: (1) perceptual, motor, and physical development; (2) social and emotional development; (3) approaches to learning; (4) language and communication; and (5) cognition. Programs can use this information as a guide to inform their practices and policies and to help them think about their theories of change and what outcomes they are focused on improving for young children.