This chapter explains the origin of the digestive system and its general parts. It explores the contributions of endoderm and splanchnic mesoderm to the development of the digestive system. The digestive and respiratory systems allow us to subsist on the food and oxygen in our environment. Our digestive system serves us in two obvious but important ways. This chapter discusses the relationship between the foregut, midgut, and hindgut of the embryo and the adult parts of the digestive system and digestion before and after birth. The chapter describes the contributions of endoderm and mesenchyme to the development of the respiratory system and the origin of the respiratory system. It also discusses the role of surfactant in lung development and its relationship to respiratory distress syndrome. Particular types of mesenchyme act in association with respiratory endoderm to develop particular regions of the respiratory system, such as the trachea or bronchi.