  As the shock and expanding shell of a supernova plow out through the
circumstellar material at thousands of km/s, radio emission is generated. VLBI
observations of this radio emission are presently the only means to directly
image the expanding shell of any supernova much farther away than SN 1987A. The
last decade has seen great progress in VLBI imaging of radio supernovae. In
particular, SN 1993J in the galaxy M81 provided a rare opportunity to closely
study an expanding supernova, and has been intensively observed. I summarize
some of the results on SN 1993J and other radio supernovae, and compare the
different observed radio supernovae. I briefly discuss the future prospects of
radio supernovae imaging.
