This document provides a review of the etiology of cleft lip and palate. It discusses that cleft lip and palate have a multifactorial etiology involving both genetic and environmental factors. Several genes have been discovered that can cause syndromic cleft lip and palate. The etiology is complex, and both genetic and environmental factors contribute, but have not been fully elucidated. Normal facial development and the pathogenesis of cleft lip and cleft palate are also reviewed.