  I outline the dynamical evolution of the shell remnants of supernovae (SNRs),
from initial interaction of supernova ejecta with circumstellar material (CSM)
through to the final dissolution of the remnant into the interstellar medium
(ISM). Supernova ejecta drive a blast wave through any CSM from the progenitor
system; as material is swept up, a reverse shock forms in the ejecta, reheating
them. This ejecta-driven phase lasts until ten or more times the ejected mass
is swept up, and the remnant approaches the Sedov or self-similar evolutionary
phase. The evolution up to this time is approximately adiabatic. Eventually, as
the blast wave slows, the remnant age approaches the cooling time for immediate
post-shock gas, and the shock becomes radiative and highly compressive.
Eventually the shock speed drops below the local ISM sound speed and the
remnant dissipates. I then review the various processes by which remnants
radiate. At early times, during the adiabatic phases, thermal X-rays and
nonthermal radio, X-ray, and gamma-ray emission dominate, while optical
emission is faint and confined to a few strong lines of hydrogen and perhaps
helium. Once the shock is radiative, prominent optical and infrared emission is
produced. Young remnants are profoundly affected by interaction with often
anisotropic CSM, while even mature remnants can still show evidence of ejecta.
