  Non-minimal renormalisation schemes such as the momentum subtraction scheme
(MOM) have frequently been used for physical computations. The consistency of
such a scheme relies on the existence of a coupling redefinition linking it to
MSbar. We discuss the implementation of this procedure in detail for a general
theory and show how to construct the relevant redefinition up to three-loop
order, for the case of a general theory of fermions and scalars in four
dimensions and a general scalar theory in six dimensions.
