  OPERA is a neutrino oscillation experiment designed to perform a nu\_tau
appearance search at long distance in the future CNGS beam from CERN to Gran
Sasso. It is based on the nuclear emulsion technique to distinguish among the
neutrino interaction products the track of a tau produced by a nu\_tau and its
decay tracks. The OPERA detector is presently under construction in the Gran
Sasso underground laboratory, 730 km from CERN, and will receive its first
neutrinos in 2006. The experimental technique is reviewed and the development
of the project described. Foreseen performances in measuring nu\_tau appearance
and also in searching for nu\_e appearance are discussed.
