  Measurement of the extragalactic background (EGBR) of diffuse gamma-rays is
perhaps one of the most challenging tasks for future gamma-ray observatories,
such as GLAST. This is because any determination will depend on accurate
subtraction of the galactic diffuse and celestial foregrounds, as well as point
sources. However, the EGBR is likely to contain very rich information about the
high energy-gamma ray sources of the Universe at cosmological distances. We
focus on the ability of GLAST to detect a signal from dark matter in the EGBR.
We present sensitivities for generic thermal WIMPs and the Inert Higgs Doublet
Model. Also we discuss the various aspects of astrophysics and particle physics
that determines the shape and strength of the signal, such as dark matter halo
properties and different dark matter candidates. Other possible sources to the
EGBR are also discussed, such as unresolved AGNs, and viewed as backgrounds.
