  Neutrino-matter cross sections and interaction rates are central to the
core-collapse supernova phenomenon and, very likely, to the viability of the
explosion mechanism itself. In this paper, we describe the major neutrino
scattering, absorption, and production processes that together influence the
outcome of core collapse and the cooling of protoneutron stars. One focus is on
energy redistribution and many-body physics, but our major goal is to provide a
useful resource for those interested in supernova neutrino microphysics.
