The origin of the cosmic, diffuse gamma ray background (EGB) is
still an open question. Amongst observed astrophysical sources,
the most promising candidate sources are star-forming galaxies,
active galaxies and potentially others including pulsars. Only
after evaluating contributions from these guaranteed sources can
one accommodate contributions from exotic sources such as
annihilating or decaying dark matter. In the light of detection
of resolved star-forming galaxies by Fermi-LAT, their unresolved
counterparts constitute an important component of the EGB as
measured by LAT. Computation of the total contribution from both
normal and starburst galaxies via various mechanisms to the EGB
in the LAT energy range shows that the total gamma-ray emission
from the star-forming universe could account for a significant
fraction of EGB for the best case model.  Even less optimistic
models remain an important contribution. The most dominant gamma
ray production mechanism as established by LAT data analysis is
from the