A wide range of conditions in the places where children live, grow, play, and learn can get "under the skin" and affect their developing brains and other biological systems. Rapidly advancing science around early childhood development provides increasingly clear evidence that, beginning before birth, these environmental conditions shape how children develop, which shapes their lifelong physical and mental health, in turn. Building upon the science presented in "Working Paper 15: Early Childhood Development and Lifelong Health Are Deeply Intertwined," this Working Paper examines how the built and natural environments--and the systemic factors that shape those environments--interact with each other and with a child's social environment in deeply interconnected ways. It explains in clear language how these environmental influences shape development and lifelong health, while also highlighting the role that current and historic public policies have played, along with systemic racism, in creating a landscape where levels of exposure to risk and access to opportunity are not distributed equally. The paper encourages us to think beyond the traditional early childhood sector in policy and practice. It explores how the latest science, combined with the lived expertise of communities and fresh thinking across an array of policy domains, offers promising opportunities for re-shaping environmental influences so that all children can grow up in homes and neighborhoods free of hazards and rich with opportunity.