Abdominal wall defects in newborns and children represent a wide spectrum of congenital and/or acquired defects ranging from simple umbilical hernias, which may spontaneously close, to very large defects, which may require the use of biosynthetic materials for a successful closure. Gastroschisis and omphalocele are the two most common congenital abdominal wall defects. They both result from failed embryonic development affecting the periumbilical abdominal wall, but they are distinct entities with different spectrum of associated pathologies. Gastroschisis results in the prolapse of small bowel and/or other abdominal organs through the relatively small congenital defect on the right side of the umbilicus. Severe associated anomalies are rare, and if the delivery is planned at the timing of less than 37 weeks of gestation, excellent outcomes are reported. Omphaloceles consist of a central abdominal wall defect with persistence of peritoneal membrane, which incorporates the umbilicus. They may range from small to gigantic, and the outcome of children is strongly dependent on the associated anomalies, which are common. Abdominal wall defects may also be acquired. A complex reconstruction may be needed to correct such defects, which are occasionally inevitable in the frame of life-saving surgical procedures. This chapter describes some basic facts about abdominal wall defects and provides information on details about treatment techniques and expected outcomes.