The Multiwavelength Approach to Unidentified Gamma-Ray Sources
  As the highest-energy photons, gamma rays have an inherent interest to astrophysicists and particle physicists studying high-energy, nonthermal processes. Gamma-ray telescopes complement those at other wavelengths, especially radio, optical, and X-ray, providing the broad, mutiwavelength coverage that has become such a powerful aspect of modern astrophysics. Multiwavelength techniques of various types have been developed to help identify and explore unidentified gamma-ray sources. This overview summarizes the ideas behind several of these methods. 
David J. Thompson