It is demonstrated that the simplified P(N) equations are a leading Or
der asymptotic limit of the transport equation. This limit is one of l
ocally nearly planar transport involving scattering which is highly pe
aked in the forward direction. This asymptotic equivalence is valid in
full generality, in that it allows time-dependent transport in a hete
rogeneous medium. It is also shown that the simplified P(N) equations
can be derived variationally, making use of certain trial functions in
a variational characterization of the even-parity transport equation.
In this case, however, there appears to be an inherent restriction to
time-independent transport in a homogeneous medium.