  SN1993J is to date the radio supernova whose evolution has been monitored in
greatest detail and the one which holds best promise for a comprehensive
theoretical-observational analysis. The shell-like radio structure of SN1993J
has expanded in general accord with models of shock excited emission, showing
almost circular symmetry for over 8 years, except for a bright feature at the
south-eastern region of the shell that has been observed at every epoch. The
spectrum of SN1993J has flattened from alpha =-1 to alpha =-0.67 (S_(\nu)
propto nu**(alpha)). The decelerated expansion can be modeled well with a
single slope but apparently better with two slopes. There are also intriguing
hints of structure in the expansion curve. The results by the two VLBI groups
carrying out this research show general agreement, but also some differences. A
comparison of the optical and VLBI results about the details of the
deceleration show some discrepancies.
