Healthy social-emotional growth in infants and toddlers, also known as infant and early childhood mental health (IECMH), provides an essential foundation for early learning, school readiness, and long-term success. Social-emotional development is intertwined with cognitive development. This connection and its role in learning can be observed in everyday behavior. An infant who joyfully participates in back-and-forth "conversation" with a parent is learning language and turn-taking skills. While trying to stack blocks, the curious, confident toddler gains motor skills and spatial knowledge. In moments like these, we see that healthy social-emotional growth propels infants and toddlers to seek out and fully engage in learning experiences through interactions with trusted caregivers and exploration of the environment. While social-emotional capacities look different at later ages, they continue to be essential to learning and positive relationships through children's school years and continuing into adult work and family life. [National Center for Children in Poverty produced this brief in partnership with the Georgia Early Education Alliance for Ready Students (GEEARS).]