Historical tour of the International Bureau of Weights and Measures (BIPM). Nestled in its green setting on the heights of the Domaine national de Saint-Cloud, the International Bureau of Weights and Measures (BIPM) is one of the oldest international organizations. It was founded on 20 May 1875 by a treaty intended "to ensure international unification and the improvement of the metric system". Known by the general public to be the guardian of the international prototypes of the meter and the kilogram, the missions of the BIPM have not stopped evolving. A hundred states are now participating in its activities. The guided historical visit of an hour to an hour and a half will allow visitors to discover the Pavillon de Breteuil (inaugurated in 1672 by Louis XIV and entrusted two centuries later to the International Bureau of Weights and Measures to settle there) and the French gardens (Grand Parterre, nursery). The BIPM’s collection of ancient instruments will allow visitors to better understand the great figures of science who have contributed to its history.