The phenomenon of superconductivity, providing current transmission without dissipation and a host of unique magnetic properties arising from macroscopic quantum coherence, was first discovered over a century ago. It was not understood until 1957, after which it quickly became clear that superconductors could in principle exist with a wide variety of the fundamental characteristic often referred to as the order parameter. Until the late 1970s, however, all superconductors found experimentally had the same class of order parameter.