The acceleration of the cosmic expansion is a fundamental
challenge to standard models of particle physics and cosmology.
The new physics of dark energy may lie in the nature of gravity
(when is gravity no longer attractive?), the quantum vacuum (does
nothing weigh something?), or extra dimensions (is nowhere somewhere?).
I present an overview of the puzzles and possibilities of dark energy
and the means for unraveling them through cosmological probes, as well
as comparing a wide variety of "beyond Lambda" models to new data.
Next generation experiments will allow us to deeply explore dark energy,
dark matter, and gravitation.