Social-emotional development and well-being are integral to the teaching and learning of literacy practices. This introductory brief focuses on the underlying science of how thinking, feeling, and perceptions along multiple dimensions interact to influence what we do as learners. This brief draws on the work of scholars in the fields of neuroscience, psychology, human development, learning sciences, literacy, and social and emotional learning (SEL) to provide a grounding framework for understanding the relationship between social-emotional development and literacy development. This brief also provides concrete examples of how supporting the five core competencies of SEL -- self-awareness, self-management, social awareness, relationship skills, and responsible decision-making -- can support students' literacy development, and vice versa. Finally, informed by the civic goals of public education, this brief also documents the relationship between social and emotional learning and literacy development are central to civic reasoning and discourse.