Herschel/HIFI reveals the first stages of stellar formation

The understanding of the star formation is still on progress. Especially, the formation of high-mass stars is much less understood than the low-mass case: even the time order of observational phenomena is uncertain. Water, one of the most important molecules in the Universe, might elucidate key episodes in the process of stellar birth, and especially could be a major role in the formation of high-mass stars. For both types of stars, the source chemical composition is not well known and even less known is the chemical evolution of the interstellar matter throughout the various phases of star formation. This talk presents the first results of the various Herschel Space Observatory star formation key-programs. One of the instruments on-board HSO, HIFI, is the most powerful spectrometer never built, covering a huge frequency range, most of them unaccessible from ground. In particular, one of the KP, WISH, aims at following the process of star formation during the various stages and at using the water as a physical diagnostic throughout the evolution.