Type Ia supernovae were long ago considered "standard candles" that
might be useful for distance measurements.  But only in the last
decade, with intense and systematic studies undertaken at CTIO and
elsewhere, was it realized that this type of supernovae are actually
more accurately "standardizable" candles.  This refinement led to an
era of precision distances that has provided solid evidence of Dark
Enery, and has changed the way both astronomers and physicists view
the Universe. We'll review the study of supernovae and their use as
cosmological tools, both in present experiments such as ESSENCE and
SNLS and future projects such as LSST.