Current knowledge of the etiology of congenital malformations of the human gastrointestinal tract is covered in this book, prefaced by some introductory notes on embryological development. Malformations involving the esophagus, stomach, small and large intestine, anus and rectum, pancreas, and hepato-billiary system are covered. There is a focus on covering those malformations for which a molecular genetic etiology is understood, but other causations, including environmental exposures, twinning, and unknown etiology are also included. For completeness, some disorders are included which are not, strictly, malformations, or which do not, strictly, involve the gastrointestinal tract. Such disorders include Hirschsprung disease, congenital diaphragmatic hernia, omphalocele, and gastroschisis. Suggested approaches to clinical evaluation of individuals with gastrointestinal malformations are included.