The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) is dedicated to the fine spectroscopy (ΔE: 2 keV FWHM @ 1 MeV) and fine imaging (angular resolution: 12' FWHM) of celestial gamma-ray sources in the energy range 15 keV to 10 MeV. INTEGRAL was selected in 1993 as the next ESA medium-size scientific mission (M2) to be launched in 2001. ESA has the overall spacecraft and mission resposibilities, Russia will provide a PROTON launcher and launch facilities, and NASA will provide ground station support through the Deep Space Network. The scientific payload complement and the INTEGRAL Science Data Centre (ISDC) will be provided by large collaborations led by Principal Investigators (PI).