The use of age-appropriate care as an organized framework for care delivery in the neonatal intensive care unit is founded on the work of Heidelise Als, PhD, and her synactive theory of development. This theoretical construct has recently been advanced by the work of Gibbins and colleagues with the "universe of developmental care" conceptual model and developmental care core measures which were endorsed by the National Association of Neonatal Nurses in their age-appropriate care of premature infant guidelines as best-practice standards for the provision of high-quality care in the neonatal intensive care unit. These guidelines were recently revised and expanded. In alignment with the Joint Commission's requirement for health-care professionals to provide age-specific care across the lifespan, the core measures for developmental care suggest the necessary competencies for those caring for the premature and critically ill hospitalized infant. Further supported by the Primer Standards of Accreditation and Health Canada, the institutional implementation of theses core measures requires a strong framework for institutional operationalization, presented in these guidelines. Part A of this article will present the background and rationale behind the present guidelines and their condensed table of recommendations.