This article deals with superconducting materials which have zero electrical resistance while carrying high electrical current densities (around 10(6) amperes per square centimeter) in high magnetic fields (up to 50 teslas). The technological importance of these materials is due to their use in the windings of loss-free electromagnets which generate high magnetic fields. Such magnets are the foundation for superconducting electrotechnology, a rapidly growing field whose applications include advanced electrical machines and fusion reactors. The article focuses primarily on the materials aspects of this new techology. A brief overview is given of the physical principles which underlie this special type of superconducting behavior, and some of the important basic parameters are examined. The technology required to adapt the materials to electromagnets is also discussed. A few concluding remarks concern future possibilities for materials that can be used in generating very high magnetic fields.