The detection of very high energy neutrinos requires very large detectors and a large overburden as a shield against the background of cosmic ray muons. ANTARES is at present the largest neutrino telescope currently under construction in the northern hemisphere. It is being built and installed at a depth of 2500 m in the Mediterranean Sea, near the Southern French coast, by a large European collaboration. A three-dimensional array of photomultipliers are used to detect the Cherenkov light emitted by neutrino- induced muons. The array, when completed, will consists of 12 lines each covering a vertical length of about 450 m and equipped with 75 photomultipliers arranged in triplets. The readout electronics is connected to an on-shore laboratory through a 42 km long electro-optical cable. The detector design, which constitutes a complex system of underwater sensors, together with preliminary technical results of the 5 lines already deployed and connected are presented.