A model for the radio emission from SN 1993J has been presented, and the
radio light curves of the supernova are found to be well fit by a
synchrotron spectrum, suppressed by external free-free absorption and
synchrotron self-absorption. A standard 
-wind is assumed, and
found to be adequate. The ratio of magnetic and thermal energy density
behind the shock, is 
. The injected electron spectrum has a
power law index of -2.1, consistent with diffusive shock acceleration,
and the number density scales with the thermal electron energy density.
The total energy density of the relativistic electrons is, if extrapolated
to 
, 
of the thermal energy density.
The free-free absorption required is consistent with previous calculations
of the circumstellar temperature of SN 1993J, 
K.