Studies on the colon not only serve medical interest or clinical purposes, but are also a subject of comparative physiology, from which much can be learned about the basic principles of physiology. Presented here are examples of research on the colonic ion transport of each vertebrate group, including the classical models of epithelia, rat and rabbit, and also the special and unique features in fish, amphibians, reptiles, birds and selected mammals such as the guinea pig. Physiology and pathophysiology of ion transport in the human large intestine are covered as well as the use of colonic cell cultures as model systems for crypt cell properties.