  We describe RAGE, the ``Radiation Adaptive Grid Eulerian''
radiation-hydrodynamics code, including its data structures, its
parallelization strategy and performance, its hydrodynamic algorithm(s), its
(gray) radiation diffusion algorithm, and some of the considerable amount of
verification and validation efforts. The hydrodynamics is a basic Godunov
solver, to which we have made significant improvements to increase the
advection algorithm's robustness and to converge stiffnesses in the equation of
state. Similarly, the radiation transport is a basic gray diffusion, but our
treatment of the radiation-material coupling, wherein we converge
nonlinearities in a novel manner to allow larger timesteps and more robust
behavior, can be applied to any multi-group transport algorithm.
