washes out spatial variations of the radiation field, its sensitivity to the choice of flux limiter, and the need for time-implicit integration (involving global matrix inversion) due to the stability properties of the parabolic diffusion equation. Two-moment transport is the next better approximation. It solves equations for the radiation energy density and momentum (i.e. the radiative flux) and requires a closure that describes the radiation pressure tensor (also known as the Eddington tensor). This closure can be analytic and based on the local values of energy density and flux (the M1 approximation). Alternatively, some codes compute a global closure based on the solution of a simplified, time-independent Boltzmann equation. The major advantage of the two-moment approximation is that its advection terms are hyperbolic and can be handled with standard time-explicit finite-volume methods of computational hydrodynamics and only the local collision terms need time-implicit updates.

    There are now implementations of multi-group two-moment neutrino radiation-hydrodynamics in multiple 2D/3D core-collapse supernova simulation codes (e.g., [@oconnor:15b; @kuroda:16; @roberts:16b]). This method may be sufficiently close to the full Boltzmann solution (in particular if a global closure is used) and appears to be the way toward massively-parallel long-term 3D core-collapse supernova simulations.

-   **Neutrino Oscillations.** Neutrinos 