This chapter provides a definition of neonatal intensive care and discusses the complex evolution of the organizational and physical NICU environment. A neonatal intensive care unit (NICU) is an inpatient medical unit specializing in the care of ill or premature infants and their families. Intensive care is a level of care with equipment and staff dedicated to a higher level of treatment and supervision than in other inpatient units. The baby incubator is the seed and heart of the NICU. Sometimes referred to as an isolette, the purpose of both the early and contemporary incubators was to provide an environment that was more hospitable to the infant than the unfiltered environment outside of the womb. The first NICU, however, spawned a negative response from the medical community. The primary focus of the physical environment of the early NICUs was to support life-saving treatments, and was not characterized by what would be described as a nurturing environment.