  One of the main scientific objectives of the recent Fermi mission is
investigating the origin of the unidentified gamma-ray sources (UGSs). Despite
the large improvements of Fermi in the gamma-ray source localization with
respect to the past gamma-ray missions, about 1/3 of the gamma-ray objects
detected do not have yet an assigned counterpart a low energies. We recently
developed a new association method to identify if there is a gamma-ray blazar
candidate within the positional uncertainty region of a generic gamma-ray
source. This method is entirely based on the discovery that blazars, the
largest known class of gamma-ray sources, can be recognized and separated from
other extragalactic sources on the basis of their infrared colors. Here we
summarize the results obtained by applying our association procedure to the
unidentified gamma-ray sources (UGSs) and to the active galaxies of uncertain
type (AGUs) listed in the Second Fermi Large Area Telescope (LAT) catalog.
