Historically, the search for the inter-galactic medium
(IGM) motivated the search for  the Far Ultraviolet (FUV) background
which in turn led to a number of experiments and missions.  Decades
later the focus shifted to FUV as the primary heating and ionizing
agent of the atomic phases (warm and cold neutral medium).  The
current view is that the diffuse FUV emission, at high latitudes,
has three components: FUV light from hot stars in the Galactic plane
reflected by dust grains (diffuse galactic light or DGL), FUV from
other galaxies (extra-galactic background light, EBL) and a component
of unknown origin.  During the eighties, there was some discussion
that decaying dark matter particles produced FUV radiation. In my
talk I systematically investigate production of FUV photons by the
Galactic Hot Ionized Medium (line emission) and two photon emission
from the  Warm Ionized Medium, the general class of low velocity
shocks and from Lyman fluorescence in the Solar System (the
interplanetary medium and  the exosphere of Earth).  I conclude
that two thirds to perhaps all of the third component can be explained
by the sum of the processes listed above.