This work covers a wide range of problems whose solution is required in order that current paradigms of melt migration (percolation, crack propagation, diapirism) can be placed on a firm foundation. This theoretical effort is complementary to existing and expected experimental efforts and geophysical data and has components of microphysics (behavior of partial melts at the lengthscale of individual grains), mesophysics (behavior at intermediate lengthscales) and macrophysics (behavior of geological systems, e.g., mid-ocean ridges, subduction zone volcanism, seamounts).