Biological cells need to maintain their internal composition different from that outside them. This is done by ion pumps which are proteins embedded in the membrane surrounding the cells. Ion pumps are found throughout the animal kingdom including bacteria. This review describes both their mechanism and some of the many uses to which they are put. Ion pumps can move ions against electrochemical gradients. They need energy to do this. In primary ion pumps the energy comes from various sources, including light, oxidation-reduction reactions and ATP. In secondary ion pumps the energy to move the ion comes from the electrochemical gradient of another ion. Ion pumps are used to bring some substances into the cell and remove others from the cell. In this way they contribute to regulating the contents of the cell. Furthermore ion pumps can be used to regulate the contents of the whole body and are therefore essential for life.