Zinc is an essential trace element. The human body contains 2-3 g of zinc. Since there are no storing systems for zinc in the body, zinc has to be ingested daily and the homeostasis has to be regulated accurately. The recommended daily intake varies between 7-12mg of zinc. The chemical properties of zinc made it to one of the favorite metal ions in biological processes. This results in hundreds of zinc-dependent enzymes and signaling events dependent on zinc. Due to this importance a deficiency in zinc is related to multiple organ dysfunctions. Since zinc deficiency has been described in humans it became more and more obvious that severe zinc deficiency is one of the leading health problems in developing countries and marginal zinc deficiency a common problem in the industrial world. Therefore a detailed knowledge about zinc is necessary to understand dysfunctions in zinc homeostasis and to develop therapies using the biological capacity of this trace element.