  ESA's INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) was launched
on 17 Oct 2002 at 06:41 CEST. Since then, it has been providing long,
uninterrupted observations (up to about 47 hr, or 170 ksec, per satellite orbit
of 2.7 days) with a large field-of-view (fully coded: 100 deg^2), msec time
resolution, keV energy resolution, polarization measurements, as well as
additional coverage in the optical. This is realized by two main instruments in
the 15 keV to 10 MeV range, the spectrometer SPI (spectral resolution 3 keV at
1.8 MeV) and the imager IBIS (angular resolution 12 arcmin FWHM), complemented
by X-ray (JEM-X; 3-35 keV) and optical (OMC; Johnson V-band) monitors. All
instruments are co-aligned to simultaneously observe the target region. A
particle radiation monitor (IREM) measures charged particle fluxes near the
spacecraft. The Anti-coincidence subsystems of the main instruments are also
efficient all-sky gamma-ray detectors, which provide omni-directional
monitoring above ~75 keV. INTEGRAL can also rapidly (within a couple of hours)
re-point and conduct Target of Opportunity observations. INTEGRAL has build an
impressive legacy: e.g. discovery of >600 new high-energy sources; first-ever
direct detection of 56Ni and 56Co radio-active decay lines from a Type Ia
supernova; new insights on positron annihilation in the Galactic bulge and
disk; pioneering gamma-ray polarization studies. INTEGRAL is also a successful
in multi-messenger astronomy: INTEGRAL found the first prompt electromagnetic
radiation in coincidence with a binary neutron star merger. More than 1750
papers based on INTEGRAL data have been published in refereed journals. Here we
give a comprehensive update of the satellite status after more than 18 years of
operations in a harsh space environment, and an account of the successful
Ground Segment.
