Neutrino astronomy is an interesting way to probe deep Universe. Indeed, despite their great success, photon observations in astrophysics suffer from limitations due to photon interaction at high energy, while cosmic ray observations are impaired by GZK effect at high energies and by proton deflection in magnetic fields at low energies. A neutrino telescope is based on Cherenkov light detection: the neutrino interaction inside large volumes of matter surrounding the detector produces charged particles leading to Cherenkov photon emission in ice or water. A neutrino telescope is an assembly of photomultipliers observing the darkness of deep‐sea or ice, and waiting for light produced by muons or showers induced by cosmic neutrinos. Several neutrino telescopes are in operation in the World: ICECUBE in the ice of the South Pole, BAIKAL in the Baikal lake, ANTARES in the Mediterranean sea. A project of a Mediterranean cubic‐kilometre‐scale neutrino telescope is under study: KM3NeT. With an instrumented volume of about 5 km3, it will have an unsurpassed sensitivity and angular resolution ‐down to 0.1 degrees at 100 TeV. We will present the characteristics of these experiments, as well as the results of their observations and expected performances.