The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite will obtain high spectral resolving power ((lambda) /(Delta) (lambda) equals 30,000) measurements of astrophysical objects in the 905 - 1195 angstroms wavelength region from low-earth orbit. The instrument's high effective area (30 - 100 cm2) and low detector background will permit observations of solar system, galactic, and extragalactic targets that have been too faint for previous instruments at this high resolution. The instrument design achieves both high resolution and high throughput by using four nearly identical optical channels. The optics consist of four normal incidence mirrors, four high density holographically-ruled diffraction gratings, and a pair of large format double delay line detectors. These components are supported by a graphite-composite structure. A commercially-procured spacecraft provides pointing stability of 0.5 arcseconds (1 (omega) ), by using data from a Fine Error Sensor included in the instrument. In early 1995 the FUSE mission was reconstructed to be a lower-cost, PI-class mission. The construction phase began in December, 1995, and launch is scheduled for late 1998. We present a description of the FUSE instrument, including details of the optical and mechanical design, along with an estimate of its on-orbit performance.