  The ANTARES collaboration is building a deep sea neutrino telescope in the
Mediterranean Sea. This detector will cover a sensitive area of typically 0.1
km-squared and will be equipped with about 1000 optical modules. Each of these
optical modules consists of a large area photomultiplier and its associated
electronics housed in a pressure resistant glass sphere. The design of the
ANTARES optical module, which is a key element of the detector, has been
finalized following extensive R & D studies and is reviewed here in detail.
