The science of early brain development tells us clearly—whether we are parents, teachers, or policy leaders—that we must pay especially close attention to children’s growth in the early years before they start school. This is the time during which the brain is growing in the most amazing ways. It is also the time when early adversity can literally change the architecture and processing of the brain, with both short- and long-term negative consequences for health, safety and learning. Science has also taught us that early brain development progresses within the context of the reciprocal, responsive relationships that very young children have with their primary adult caregivers.