As thorough readers of this book have begun to discover by this chapter on metrology, the most widely used applications of superconducting electronics involve measurements of electromagnetic phenomena. Unlike most other phenomena used for measurements, superconductivity is also essential for electrical standards. Because it is a quantum phenomenon, it can represent voltage in terms of fundamental constants with an amazing precision of a few parts in 1019. In some regards superconducting voltage standards based on arrays of Josephson junctions are the most successful application of superconductivity, considering the numbers of junctions and their worldwide use. While they are conceptually simple, it has taken almost 50 years for their underlying technology to progress from unreliable single junctions to robust, complex, three-dimensional integrated circuits having more than 300,000 junctions and producing precision ac voltages up to 10 V. Here is their story.