  So far radial velocity (RV) measurements have discovered ~25 stars to host
multiple planets. The statistics imply that many of the known hosts of
transiting planets should have additional planets, yet none have been solidly
detected. They will be soon, via complementary search methods of RV,
transit-time variations (TTV) of the known planet, and transits of the
additional planet. When they are found, what can transit measurements add to
studies of multiplanet dynamical evolution? First, mutual inclinations become
measurable, for comparison to the solar system's disk-like configuration. Such
measurements will give important constraints to planet-planet scattering
models, just as the RV measurements of eccentricity have done. Second, the
Rossiter-McLaughlin effect measures stellar obliquity, which can be modified by
two-planet dynamics with a tidally evolving inner planet. Third, TTV is
exquisitely sensitive to planets in mean motion resonance. Two planets
differentially migrating in the disk can establish such resonances, and tidal
evolution of the planets can break them, so the configuration and frequency of
these resonances as a function of planetary parameters will constrain these
processes.
