A proof of transient fluctuation relations for the entropy
production (dissipation function) in nonequilibrium systems, is
provided that is valid for most time reversible dynamics. The
conditions under which a transient fluctuation relation yields a
steady state fluctuation relation for driven nonequilibrium systems
whose transients relax, producing a unique nonequilibrium steady state
will then be considered. Although the necessary and sufficient
conditions for the production of a unique nonequlibrium steady state
are unknown, if such a steady state exists, the generation of a steady
state fluctuation relation from the transient relation is shown to be
very general. It is essentially a consequence of time reversibility
and of a form of decay of correlations in the dissipation, which is
needed also for, e.g., the existence of transport coefficients.
Because of this generality the resulting steady state fluctuation
relation has the same degree of robustness as do equilibirum
thermodynamic equalities.