  Discoveries in the last few years have revolutionized our knowledge of the
universe and our ideas of its ultimate fate. Measurements of the expansion of
the universe show that it is not slowing down under normal gravity but
accelerating due to an unknown, gravitationally repulsive ``dark energy''. This
may be a clue to new properties of quantum physics or of gravity beyond
Einstein. I present an overview of the puzzles of dark energy and the means for
unraveling them through cosmological probes, on both a generally accessible and
a technical level. I also highlight the strong benefits of meshing supernova
distance and weak lensing methods. Next generation experiments such as the
Supernova/Acceleration Probe (SNAP) satellite would measure the supernova
distance-redshift relation to high accuracy and map the evolution of structure
and dark matter through gravitational lensing. These observations will explore
the frontiers of physics and aim to uncover what makes up the still unknown 95%
of our universe.
