Extremely Red Galaxies: Old or Dusty ?
  The nature of the extremely red galaxies is poorly known, the critical issue being whether they are old ellipticals at $z>1.5$ or distant star-forming galaxies strongly reddened by dust extinction. Here we review the little we know about them, and we present recent and preliminary results from our ongoing submillimeter -- millimeter observations. 
Andrea Cimatti (Arcetri), Paola Andreani (Padova and MPE), Huub   R\"ottgering (Leiden), Remo Tilanus (JACH and NFRA)