This paper, the first in a series on early childhood development, updates and expands on previous research and global commitments to early childhood development. It highlights the urgent need to increase multisectoral coverage of quality programming that incorporates health, nutrition, security, safety, responsive caregiving, and early learning. The paper examines recent scientific progress and global commitments to early childhood development, emphasizing the importance of a life course perspective. It discusses the impact of adversity and nurturing care on brain development and function throughout the life course. The paper also reviews global commitments and progress in early childhood development since 2000, assesses access to center-based and home-based early childhood development programs, and describes cross-sectoral opportunities to implement early childhood development programs. It concludes by emphasizing the need for population-level indicators of child development and the importance of ensuring adequate health, nutrition, security, safety, responsive caregiving, and early learning opportunities for young children to achieve the Sustainable Development Goals.This paper, the first in a series on early childhood development, updates and expands on previous research and global commitments to early childhood development. It highlights the urgent need to increase multisectoral coverage of quality programming that incorporates health, nutrition, security, safety, responsive caregiving, and early learning. The paper examines recent scientific progress and global commitments to early childhood development, emphasizing the importance of a life course perspective. It discusses the impact of adversity and nurturing care on brain development and function throughout the life course. The paper also reviews global commitments and progress in early childhood development since 2000, assesses access to center-based and home-based early childhood development programs, and describes cross-sectoral opportunities to implement early childhood development programs. It concludes by emphasizing the need for population-level indicators of child development and the importance of ensuring adequate health, nutrition, security, safety, responsive caregiving, and early learning opportunities for young children to achieve the Sustainable Development Goals.