First an introduction to the basic principles of heavy ion storage rings is given, which considers the conditions for storing fast moving ions in the periodic structure of a ring given by the magnetic elements. Laser cooling and electron cooling are discussed as alternative cooling schemes and cooling results from the presently operating storage rings will be shown. The use of the high‐quality electron beam in the cooler for electron‐ion collision experiments will be demonstrated with examples of electron impact excitation and ionization, radiative, dielectronic, and collisional (three‐body) recombination, and laser stimulated recombination. We also give an overview on the different heavy‐ion storage rings running already and starting‐up in different accelerator laboratories.