  FIRBACK is one of the deepest cosmological surveys performed in the far
infrared, using ISOPHOT. We describe this survey, its data reduction and
analysis. We present the maps of fields at 175 microns. We point out some first
results: source identifications with radio and mid infrared, and source counts
at 175 microns. These two results suggest that half of the FIRBACK sources are
probably at redshifts greater than 1. We also present briefly the large
follow-up program.
