  Measurements of the distances to SNe Ia have produced strong evidence that
the expansion of the Universe is accelerating, implying the existence of a
nearly uniform component of dark energy with negative pressure. We show that
constraints to this mysterious component based upon large-scale structure
nicely complement the SN Ia data, and that together they require Omega_X =
(0.6,0.7) and w_X < -0.6 (95% cl), for the favored flat Universe. Other
cosmological data support this conclusion. The simplest explanation, a
cosmological constant, is consistent with this, while some of the other
possibilities are not.
