We review HOM interference and explore a new physical entity: The Two-Photon or Biphoton. This Two-Photon is product of Parametric Down-Conversion (PDC) and its existence is a new evidence of quantum entanglement. This entanglement, on energy and momentum, besides on polarization allow us to produce any of the four Bell’s states [ref 12]. Finally, the HOM interference can be used to develop Bell’s State Measurements (BSM) and distinguish one of Bell’s States [ref 5]; this is a very important feature to use it in new fields of applications of quantum mechanics.