Investing in young children is one ofthe best investments that countries can make. A child searliest years present a unique window of opportunity toaddress inequality, break the cycle of poverty, and improvea wide range of outcomes later in life. Recent brainresearch suggests the need for holistic approaches tolearning, growth, and development, recognizing that youngchildren s physical and intellectual well-being, as well astheir socio-emotional and cognitive development, areinterrelated. To fully benefit from future opportunities inlife and become productive members of society, by the end ofearly childhood, young children must be: healthy andwell-nourished; securely attached to caregivers; able tointeract positively with families, teachers, and peers; ableto communicate in their native language; and ready to learnthroughout primary school. This document draws on theseexisting frameworks and broad evidence on the impacts of ECDinterventions. It summarizes some of the existing literatureon this topic with the aim to identify key interventionsneeded for children. The document is intended to provide aneasily accessible introduction to interventions andintegrated services that could help policymakers andpractitioners think about how to effectively invest in ECD.In addition to identifying key interventions, the documentoutlines four principles that can help countries design andimplement strong ECD policies and programs. Countriesshould: (i) prepare an ECD diagnostic and strategy; (ii)implement widely through coordination; (iii) createsynergies and cost savings through integrated interventions;and (iv) monitor, evaluate, and scale up successfulinterventions. In terms of interventions, within the ECDperiod, 25 key interventions are identified as essential fora child s growth and development. For each intervention,illustrative costs and impacts are provided. These are basedon existing evidence and are only intended to be indicative.The document suggests that these interventions can bedelivered through five integrated packages at differentstages in a child s life. The five packages of interventionsinclude: (a) the family support package, which should beprovided throughout the ECD period, (b) the pregnancypackage, (c) the birth package (from birth to six months),(d) the child health and development package, and (e) thepreschool package.