The International System of Units (SI from the French Le Système International d’Unités) is the universally accepted method of expressing physical measurements for world commerce, industry, and science. Though officially established in 1960, the origins of the present SI can be traced back to the creation of the decimal Metric System during the French Revolution. The SI has proven to be a living, evolving system, changing as new knowledge and measurement needs arise, and once again international consensus is building to advance the SI to reflect contemporary understanding of the physical world. The new framework of the future SI will no longer be based on definitions of units such as the meter, kilogram, and second. Instead it will adopt exact values for seven fundamental constants of nature upon which all SI units will be realized. Gone are the base units and their definitions.