  We introduce a speed selection mechanism for front propagation in
reaction-diffusion systems with multiple fields. This mechanism applies to
pulled and pushed fronts alike, and operates by restricting the fields to large
"finite" intervals in the comoving frames of reference. The unique velocity for
which the center of a monotonic solution for a particular field is insensitive
to the location of the ends of the finite interval is the velocity that is
physically selected for that field, making thus the solution approximately
translation invariant. The fronts for the various fields may propagate at
different speeds, all of them being determined through this mechanism. We
present analytic results for the case of piecewise parabolic potentials, and
numerical results for other cases.
