Origins and history of the International System of Units, SI

This paper outlines the origins and history of the International System of Units with particular reference to the historical development of units based on fundamental constants or invariants of nature. In the past, the ideas and the intention to proceed towards a unit system based on invariants of nature had existed but it has only recently become a practical possibility. The adoption by the 24^th General Conference on Weights and Measures of a Resolution outlining the principles of such a system is the culmination of more than two hundred years of advances in physics and metrology.