CGPM, in French is "de Conference Generale des Poids et Measures", known as the "General Conference of Weights and Measures" in English. It was formed in 1875 when a group of industrialized nations signed the "Treaty of the Meter", after much debate and dicussion in order that standards of measurements, both physical and treaty based, would be on a common basis between the signatory countries.
The BIPM, Bureau International des Poids et Measures (International Bureau of Weights and Measures, located in Serves, France, is the scientific branch of a three part organisation that includes the CGPM and the CIPM. The CGPM holds regular meetings to regulate the measurement side of world commerce through updates to the Treaty as well as activities such as international intercomparisons of physical standards and more mundane things like bugeting.
The CIPM is the Comite International des Poids et Measures, or International Committee of Weights and Measures made up of 18 members out of body of the CIPM. The CIPM receives, organises and presents proposed items to the CGPM for a vote by all signatory members.
It may be of interest that of the seven basic units of measurements, from which all other units may be derived, the kilogram is the last to be based on an artifact rather than a repeatable natural phenomena. The artifact is called "Le Grande K" and is kept under tightly controlled conditions in a bomb proof safe in Serves. Experiments are underway to rectify this situation using Avagadro's Number or the watt balance (a variation of the balance used to determine the ampere). An uncertainty of less than 1 part in 10 billion must be realized to replace the comparison methods that have an uncertainy at least equal to that or less if done in vacuo.
The United States has been a member since the inception of the Treaty of the Meter and responsibility for measurements reside within the National Institute of Standards and Technology (NIST). In particular, the maintenence and dissemination of the mass unit is a function of the Mass and Force Group.
Much more information can be gleaned from the BIPM.org and the NIST.gov websites.