Herschel and the TeraHertz sky

Herschel is a spatial submillimetre observatory with spectroscopic and imaging capabilities covering the range from 55 to 671 μm (0.44 to 5.5 THz) partly explored for the first time here. With a primary mirror of 3.5 m, it is presently the largest telescope launched. Its primary targets are the cold dust, the light hydrides, with a special focus on H2O, and a few species of high interest like C+ and O2 in both our Galaxy and other galaxies. Its main focus is on star formation in all its possible aspects including cosmological metal enrichment evolution, statistics on prestellar cores or chemistry of protostar outflow terminal shocks to name only a few. We will describe the telescope and its three instruments, a selection of general results and we will focus on one typical case in greater detail, the observation of water in massive star forming regions. Herschel was launched in May 2009 and should function 3.5 years.