  The COBE FIRAS data contain foreground emission from interplanetary, Galactic
interstellar dust and extragalactic background emission. We use three different
methods to separate the various emission components, and derive the spectrum of
the extragalactic Far InfraRed Background (FIRB). Each method relies on a
different set of assumptions, which affect the FIRB spectrum in different ways.
Despite this, the FIRB spectra derived by these different methods are
remarkably similar. The average spectrum that we derive in the \nu = 5 - 80
cm^{-1} (2000-125 \um) frequency interval is: I(\nu) = (1.3 \pm
0.4)\times10^{-5} (\nu /\nu_0)^{0.64 \pm 0.12} P_{\nu}(18.5 \pm 1.2 K), where
\nu_0=100 cm^{-1} (\lambda_0=100 \um) and P is the Planck function. The derived
FIRB spectrum is consistent with the DIRBE 140 and 240 \um detections. The
total intensity received in the 5 - 80 cm^{-1} frequency interval is 14 nW
m^{-2} sr^{-1}, and comprises about 20% of the total intensity expected from
the energy release from nucleosynthesis throughout the history of the universe.
