  Observations show that Type Ia Supernovae (SNe Ia) form a homogeneous class
of objects. They share similar spectroscopic evolution, light-curve shapes, and
peak absolute magnitudes. The slight departures from homogeneity that are
observed can be used to produce a "calibrated candle" with corrected magnitudes
with even smaller dispersion. The existence of this intrinsically bright
distance indicator has inspired two coordinated high-redshift supernova
searches: the Supernova Cosmology Project and the High-z Supernova Search Team.
To date ~100 SNe Ia have been discovered by the two groups. The preliminary
analysis of the first of these objects demonstrate how well SNe Ia can be used
to measure the mass density of the universe Omega_M and the normalized
cosmological constant Omega_Lambda = Lambda/3H_0^2.
