The neonatal period refers to the first 4 weeks of life beginning at birth. This is a vulnerable time period for a neonate’s health and development. Infant mortality most often occurs during the neonatal period. According to the World Health Organization, internationally, 44% of infant deaths under the age of 5 occur during the first 4 weeks of life. This entry provides insight into neonatal health and development issues, including nutrition, reflexes, and sleeping patterns, and outlines several approaches to neonatal assessment.