Pediatrics (also spelled paediatrics) is the branch of medicine that deals with the medical care of infants, children, and adolescents (from newborn to age 18-21). The word pediatrics is derived from two Greek words paidi (παιδί) which means "boy" and iatros (ιατρός) which means "doctor". Most pediatricians are members of a national body, such as the American Academy of Pediatrics, the Canadian Paediatric Society, the British Association of Paediatric Surgeons, the Royal College Of Paediatrics and Child Health, Norsk barnelegeforening (The Norwegian society of pediatricians) or the Indian Academy of Pediatrics

Pediatrics differs from adult medicine in many respects. The obvious body size differences are paralleled by maturational changes. The smaller body of an infant or neonate is substantially different physiologically from that of an adult. Congenital defects, genetic variance, immunology, oncology, and a host of other issues are unique to the realm of pediatrics. Increasingly effective health care also means that diseases such as sickle cell anemia and cystic fibrosis are more often treated by pediatricians, though many or most patients grow into adulthood. Issues revolving around infectious diseases and immunizations are also dealt with primarily by pediatricians.

Pediatrics is also a springboard for any specialty of general medicine, each with its own unique aspects. Pediatric cardiologists deal with heart conditions in children, particularly congenital heart defects, pediatric oncologists often treat leukemias and lymphomas. Every subspecialty of the adult doctor exists in the pediatric field (with the exception of geriatrics), but some are unique to pediatrics, such as adolescent medicine, sports medicine, and neonatology.