The Mystery of Unidentified Infrared Emission Bands
  A family of unidentified infrared emission (UIE) bands has been observed
throughout the Universe. The current observed spectral properties of the UIE
bands are summarized. These properties are discussed in the frameworks of
different models of the chemical carriers of these bands. The UIE carriers
represent a large reservoir of carbon in the Universe, and play a significant
role in the physical and chemical processes in the interstellar medium and
galactic environment. A correct identification of the carrier of the UIE bands
is needed to use these bands as probes of galactic evolution.
