Supersymmetric extensions of the standard model appear today either as viab
le alternatives or as testing grounds for the range of its validity. The pr
oper renormalization of supersymmetry is therefore needed. First its formul
ation for supersymmetric QED is presented and then a clarification of the s
tatus of the symmetry on the operator level. Supersymmetry is seen to hold
only on the physical Hilbert space.