The Origins Space Telescope (OST) will transform our understanding of the Universe, from formation of the earliest galaxies to the creation of habitable worlds. OSTs Mission Concept 1, the subject of this report, features a cold (4 K) large-aperture telescope (9.1 m) and five powerful instruments, providing imaging and spectroscopy over a wavelength range from 5 to 660 microns. OSTs dramatic increase in sensitivity over previous missions ensures breakthrough discoveries in a broad range of astrophysics disciplines.