Sepsis is a significant cause of mortality and morbidity in newborn infants. Depending on the timing of symptoms and signs, sepsis during the neonatal period classically is divided into early-onset sepsis and late-onset sepsis. Primary risk factors for early-onset sepsis are prematurity, low birth weight, prolonged rupture of membranes, chorioamnionitis, and maternal colonization with group B streptococcus. In late-onset sepsis, maternal obstetric complications are rare and the main risk factors for sepsis are the procedures carried out in hospital to keep the infant alive. This article reviews the classification, pathogenesis, etiology, epidemiology, clinical findings of neonatal sepsis and current knowledge regarding the diagnosis and treatment of neonatal sepsis.