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The International System of Units (abbreviated SI from French: Le Système international d'unités) is the modern form of the metric system and is the world's most widely used system of measurement, used in both everyday commerce and science. It comprises a coherent system of units of measurement built around seven base units, 22 named and an indeterminate number of unnamed coherent derived units, and a set of prefixes that act as decimal-based multipliers.
The standards, published in 1960 as the result of an initiative started in 1948, are based on the metre–kilogram–second system, rather than the centimetre–gram–second system, which, in turn, had several variants. The SI has been declared to be an evolving system; thus prefixes and units are created and unit definitions are modified through international agreement as the technology of measurement progresses, and as the precision of measurements improves.
The driving force behind the development of the Système international was the diversity of units that had sprung up within the CGS system of units and the lack of coordination between the various disciplines that made extensive use of units of measurement. In addition to defining a new realisation of the metric system, the General Conference on Weights and Measures, an organisation set up by the Convention of the Metre in 1875, succeeded in bringing together many of the leading international organizations to agree not only the definitions of the SI, but also rules on writing and presenting measurements in a standardised manner around the globe.
The system has been adopted nearly globally. Only Burma, Liberia and the United States have not adopted SI units as their official system of weights and measures. In the United States metric units are not commonly used outside of science, medicine and the government; however, United States customary units are officially defined in terms of SI units. The United Kingdom has officially adopted a partial metrication policy, with no intention of replacing imperial units entirely. Canada has adopted it for most purposes, but imperial units are still legally permitted and remain in common use throughout a few sectors of Canadian society, particularly in the buildings, trades and railways sectors. 

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