The Josephson effect, the 50th anniversary of which will be celebrated in 2012, remains one of the most spectacular manifestations of quantum mechanics in all of experimental science. It was first predicted in 1962 and then experimentally verified in 1963. At its most fundamental level the Josephson effect is nothing more than the electronic analogue of interference phenomena in optical physics. But from this humble premise springs a huge range of physical phenomena and electronics applications which placed Josephson devices at the heart of physics research during the second half of the century of superconductivity and beyond. This article gives a summary of both the physics underlying the effect and current and possible future applications of Josephson devices and superconducting quantum interference devices (SQUIDs). (Contains 4 figures and 3 footnotes.)