In anatomy of the digestive system, the cecum or caecum is a pouch connected to the large intestine between the ileum and the colon. It is separated from the ileum by the ileocecal valve (ICV) or Bauhin's valve, and is considered to be the beginning of the large intestine and part of the colon.

Its primary function is to absorb water and salts from undigested food. It has a muscular wall that can knead the contents to enhance absorption.

The cecum is present in mammals, birds, and some reptiles. Herbivores have a larger cecum than humans, and exclusive carnivores have a smaller cecum or none at all. This size difference results from the large number of bacteria in the cecum of herbivores, which aid in the enzymatic breakdown of plant materials such as cellulose. Carnivores, whose diets contain little or no plant material, have a reduced cecum, often partially or wholly replaced by the vermiform appendix.

The appendix is a branch of the cecum. Like the appendix, the cecum (from the Latin caecus meaning blind) was once believed to have no function.