  A new method for constructing flows between distinct Landau-Ginzburg theories
at fixed central charge is presented. The essential ingredient of the
construction is an enlarged moduli space obtained by adding theories with zero
central charge. The flows involve only marginal directions hence they can be
applied to transitions between string vacua, in particular to the construction
of mirror pairs of string ground states described by RG fixed points of N=2
supersymmetric Landau--Ginzburg theories. In contrast to previous methods this
new construction of mirror theories does not depend on particular symmetries of
the original theory.
