Optical fibre sensors (OFS) are now seen as a rapidly developing technique with the potential to meet the increasing needs of the nuclear power plants of Electricite de France (EDF), as far as optimal maintenance is concerned. Their use in networks (OFSN) of various types (parallel, series, ring, . . .) allows effective monitoring and control of major components in the power station (nuclear reactor, generator, pumps, pipes, . . .). EDF is carrying out several applications through its own R&D efforts and cooperation with many scientific laboratories and industrial companies.