  Extending previous work in Randall-Sundrum type models, we construct
low-energy effective actions for braneworlds with a bulk scalar field, with
special attention to the case of BPS branes. Holding the branes at fixed
coordinate position with a general ansatz for the bulk metric, and imposing the
Einstein frame as a gauge condition, we obtain a scalar-tensor theory with only
one scalar degree of freedom related to the proper brane separation. The
formalism is applicable even when there is direct coupling of the bulk scalar
and brane matter, as in the Horava-Witten model. We further show that the usual
moduli space approximation actually describes a non-BPS three-brane system.
