The mission of the International Council for Science : Committee on Data for Science and Technology (CODATA ) is to strengthen international science for the benefit of society by promoting improved scientific and technical data management and use. One of their most visible outputs comes from the Working Group on Fundamental Physical Constants, who periodically perform a comprehensive least squares adjustment and produce the well-known and widely cited publication entitled "Internationally recommended values of the Fundamental Physical Constants" (freely available at http://physics.nist.gov/cuu/constants
). When the proposed changes to the International System of Units (SI) to use fixed values for some fundamental constants take effect in the coming years, it will be the responsibility of this CODATA Working Group to provide the final values for Planck's constant, h, Avogadro's constant, NA, the fundamental electronic charge, e, and the Boltzmann constant, k, that will be used. In this presentation, the least squares adjustment procedure will be outlined and illustrated with reference to the current state-of-the- art measurements in several physical disciplines.