  For some years there has been uncertainty over whether regularisation by
dimensional reduction (DRED) is viable for non-supersymmetric theories. We
resolve this issue by showing that DRED is entirely equivalent to standard
dimensional regularisation (DREG), to all orders in perturbation theory and for
a general renormalisable theory. The two regularisation schemes are related by
an analytic redefinition of the couplings, under which the $\b$-functions
calculated using DRED transform into those computed in DREG. The $S$-matrix
calculated using DRED is numerically equal to the DREG version, ensuring that
both schemes give the same physics.
