Acting alone, psychologists rarely achieve population impact on important mental health and well-being outcomes for families and young children. The traditional Institute of Medicine model of moving from efficacy trials to effectiveness trials to scaling up has not succeeded, partly due to degradation of program quality and impact during scale-up and partly due to a failure to consider system-context issues at the outset. Analysis of barriers to population impact leads to the proposal of a new comprehensive system of care that includes both top-down coordination among community agencies providing services and bottom-up outreach to every family to connect them with services. The North Carolina Smart Start Initiative is a top-down approach to improving the community-level quality of early childcare and education services. A natural experiment demonstrates that it improves population indicators of children's education outcomes. Family Connects is a bottom-up approach that reaches all families giving birth in a community through brief home visits to assess needs and connect families with community resources. A randomized controlled trial reveals increased community connectedness, lower maternal anxiety, reduced emergency health episodes, and lower rates of investigations for child abuse. These initiatives point toward the promise of population impact through psychological interventions in early life that are delivered in a collaborative system of care. (PsycINFO Database Record (c) 2018 APA, all rights reserved).