Newborns and young infants present an immature immune system, which makes them more susceptible to infectious agents present during this period. It is known that newborns are more vulnerable to infections than children and adults. Observed differences in the innate and adaptive immunity are responsible for decreased neonate’s defenses. The defects in the adaptive immunity require previous contact with antigens, while the innate system requires no prior immune experience. The innate immunity is the first line of defense against pathogens and is composed by the responses from granulocytes, monocytes, macrophages, and dendritic and natural killer cells. Some pathogens, responsible for intra-uterus, intra-partum, and postpartum infections stimulate fetal and neonatal immune responses. These agents include the group B streptococcus, Escherichia coli, Listeria monocytogenes, herpes simplex virus, Cytomegalovirus, Epstein-Barr virus, varicella-zoster virus, respiratory syncytial virus, Toxoplasma gondii, and Candida albicans. A better understanding of the functioning of the immune system in the neonatal period allows the doctor to perform preventive and therapeutic measures that improve the care of infections during this period. This review aims to discuss recent advances and current understanding on the newborn’s immunity focusing on immunological aspects reThe newborn’s immune system Lilian Martins Oliveira Diniz1 Bruna de Campos Guimaraes e Figueiredo2 1 Doutora em Ciencias da Saude: Medicina da Crianca e do Adolescente. Professora Adjunta do Departamento de Pediatria da Faculdade de Medicina da Universidade Federal de Minas Gerais (UFMG). Membro do Grupo de Infectologia Pediatrica da Faculdade de Medicina da UFMG. Belo Horizonte, MG – Brasil. 2 Pediatra e Imunologista. Hospital Mater Dei. Belo Horizonte, MG – Brasil. O sistema imunologico do recem-nascido DOI: 10.5935/2238-3182.20140056