Recent direct evidence from type Ia supernovae and indirect evidence from other cosmological measurements imply the existence of dark energy -- a smooth component that makes the expansion of the universe accelerate and which makes up about 70% of its energy density. Dark energy is very mysterious; its nature and its properties are poorly understood. In this talk I review the conundrums that dark energy presents to particle physics. I further address the methods to constrain the properties of dark energy using present and future cosmological probes, such as measurements of the distance-redshift relation, cosmic microwave background measurements, and large-scale structure surveys. I also discuss more general ways to characterize the evolution of the universe, and therefore test alternative dark-energy models, between redshift of zero and 1010.
