The Cosmic Origins Spectrograph (COS) was installed in the Hubble Space Telescope in May, 2009 as part of Servicing Mission 4 to provide high sensitivity, medium and low resolution spectroscopy at far- and near-ultraviolet wavelengths (FUV, NUV). COS
is the most sensitive FUV/NUV spectrograph flown to date, spanning the wavelength range from 900{AA} to 3200{AA} with peak effective area approaching 3000 cm^2. This paper describes instrument design, the results of the Servicing Mission Orbital Verification (SMOV), and the ongoing performance monitoring program.
