It has recently been realized that there is more than one kind of superconductor, and we now recognize superconducting metals and alloys as being either ‘type-1’ or ‘type-2’. The ‘new’ type-2 superconductors can exist in a state which allows them to carry isrestanceless currents even in very strong magnetic fields, and they are used to construct very powerful electromagnets. This article describes the properties of type-2 superconductors, why very strong magnetic fields are required to drive them normal and why under certain circumstances they can carry large lossless currents.