The neonatal period represents a critical stage in human development, covering the first 28 days of life. During this time, the newborn undergoes rapid physiological adaptation from intrauterine to extrauterine life. This article discusses the characteristics of the neonatal period, common physiological (transitional) conditions, the concept of newborn maturity, and the clinical signs of prematurity according to international classifications. Understanding these aspects is essential for early diagnosis, appropriate management, and reduction of neonatal morbidity and mortality.