  The large majority of EGRET point sources remain without an identified
low-energy counterpart, and a large fraction of these sources are most likely
extragalactic. Whatever the nature of the extragalactic EGRET unidentified
sources, faint unresolved objects of the same class must have a contribution to
the diffuse extragalactic gamma-ray background (EGRB). Understanding this
component of the EGRB, along with other guaranteed contributions from known
sources, is essential if we are to use this emission to constrain exotic
high-energy physics. Here, we follow an empirical approach to estimate whether
a potential contribution of unidentified sources to the EGRB is likely to be
important, and we find that it is. Additionally, we show how upcoming GLAST
observations of EGRET unidentified sources, as well as of their fainter
counterparts, can be combined with GLAST observations of the Galactic and
extragalactic diffuse backgrounds to shed light on the nature of the EGRET
unidentified sources even without any positional association of such sources
with low-energy counterparts.
