Over the last 30 years, metrology laboratories have utilized the accuracy of the Josephson effect to produce voltages calculated from first principles at DC, and more recently at AC for frequencies up to several megahertz. Josephson voltage standards provide a primary realization of the volt, the unit of electromotive force, and have improved voltage metrology by over six orders of magnitude compared to the electrochemistry-based Weston standard cells.

We will review the present status of the research and development for Josephson voltage standards and their applications. The emphasis of the talk will be on the device requirements posed by applications. The talk will conclude with a discussion on the perspectives and directions of Josephson voltage standards.