The Constellation X-ray Mission is a high throughput X-ray facility emphasizing observations at high spectral resolution(E/&Dgr;E∼300–3000),and broad energy bandpass (0.25–40 keV). Constellation-X will provide a factor of nearly 100 increase in sensitivity over current high resolution X-ray spectroscopy missions. It is the X-ray astronomy equivalent of large ground-based optical telescopes such as the Keck Observatory and the ESO Very Large Telescope. When observations commence toward the end of next decade, Constellation-X will address many fundamental astrophysics questions such as: the formation and evolution of clusters of galaxies; constraining the baryon content of the Universe; determining the spin and mass of supermassive black holes in AGN; and probing strong gravity in the vicinity of black holes. ©1999 American Institute of Physics.