  I review the current understanding of the origin and nature of ``warm''
ionized gas in giant elliptical galaxies in the light of results of recent
imaging and spectroscopic surveys. CCD imaging surveys have revealed that
emission-line disks or filaments are (as a rule) associated with dust
absorption, even in the X-ray brightest systems. This strongly suggests that
the origin of this ionized gas is generally not through ``cooling flows'';
galaxy interactions are favored instead.
  Using data from a new spectrophotometric survey of ``normal'' elliptical
galaxies covering the whole optical range, the extended ionized gas in giant
ellipticals is found to be --without exception-- of the LINER class, and most
probably NOT powered by star formation activity. I discuss two independent
pieces of evidence which suggest that the extended gas in giant ellipticals is
ionized by means of a distributed source of ionization: (i) A significant
correlation exists between the H-alpha+[NII]luminosity and the optical
luminosity within the region occupied by the ionized gas, and (ii) the
ionization parameter of the gas does not change significantly with
galactocentric radius. Two potential sources of ionization are evaluated:
Photoionization by old hot stars (of post-AGB and/or AGB-Manque' type) and
mechanical energy flux from electron conduction in hot, X-ray-emitting gas.
