  I briefly discuss the challenges presented by attempting to modify general
relativity to obtain an explanation for the observed accelerated expansion of
the universe. Foremost among these are the questions of theoretical consistency
- the avoidance of ghosts in particular - and the constraints imposed by
precision local tests of gravity within the solar system. For those models that
clear these highly constraining hurdles, modern observational cosmology offers
its own suite of tests, improving with upcoming datasets, that offer the
possibility of ruling out modified gravity approaches or providing an
intriguing hint of new infrared physics. In the second half of the talk, I
discuss a recent approach to extracting cosmology from higher-dimensional
induced gravity models.
