The Metre Convention of 1875 created the first international scientific institute, the International Bureau of Weights and Measures, which signaled the beginning of modern metrology. This chapter outlines the origins of the Convention and traces its development to the present day, including the development of the International System of Units (SI), its revision in 2018, the National Metrology Institutes and the mutual recognition arrangement put in place in 1999 to assure a documented worldwide uniformity in measurement under the Metre Convention.