 Arrays of thousands of optical sensor modules will detect the faint light in the deep sea from charged particles originating from collisions of the neutrinos and the water or rock in the vicinity of the detector.The research infrastructure will also house instrumentation for other sciences like marine biology, oceanography and geophysics for long-term and on-line monitoring of the deep-sea environment and the sea bottom at depth of several kilometres.Once fully completed, the KM3NeT research infrastructure will consists of several large subdetectors.