Long baseline neutrino oscillations experiment. The OPERA detector is placed in the LNGS underground laboratory and exposed to the
CERN CNGS nu-mu beam at 730 km from the source. the aim is to detect the apparition of nu-tau through their interactions nu-tau +
N -> tau + X via the localisation of the tau decay. The 1250 tons instrumented target is made of elements composed of lead sheets
providing the mass and emulsion films providing the resolution. The target is complemented by electronic detectors: trackers,
calorimeters and spectrometers