  Study of radio supernovae over the past 25 years includes two dozen detected
objects and more than 100 upper limits. From this work it is possible to
identify classes of radio properties, demonstrate conformance to and deviations
from existing models, estimate the density and structure of the circumstellar
material and, by inference, the evolution of the presupernova stellar wind. It
is also possible to detect ionized hydrogen along the line of sight, to
demonstrate binary properties of the stellar system, to detect clumpiness of
the circumstellar material, and to put useful constraints on the progenitors of
undetected Type Ia supernovae.
