A standard model of cosmology is emerging (often dubbed the Concordance Model), in which the universe consists of 5% ordinary baryonic matter, ∼ 26% dark matter, and ∼ 69% dark energy. [1, 2] The baryonic content is well-known, both from element abundances produced in primordial nucleosynthesis roughly 100 seconds after the Big Bang, and from measurements of anisotropies in the cosmic microwave background (CMB). The evidence for the existence of dark matter is overwhelming, and comes from a wide variety of astrophysical measurements.