Superconducting electronics was born in a remarkably short, three-year period that began one-half century after the discovery of superconductivity. The crucial steps were the observation of flux quantization in 1961, the prediction and observation of Josephson tunneling in 1962 and 1963, respectively, and the demonstration of quantum interference in a superconducting ring containing two Josephson junctions in 1964. The first practical SQUIDs (Superconducting Quantum Interference Devices) were primitive by today’s standards, and included machined, point-contact junctions and a blob of solder frozen around a length of niobium wire. Today’s SQUIDs, fabricated from patterned, multilayer thin films on silicon wafers, offer extraordinary sensitivity to magnetic flux. SQUIDs are amazingly diverse, with applications that include physics, chemistry, biology, medicine, materials science, geophysics, cosmology and quantum information. I describe experiments to search for the axion—a candidate particle for cold dark matter— and to perform magnetic resonance imaging (MRI) in magnetic fields of typically 100 microtesla, four orders of magnitude below that for conventional MRI systems.