The Usefulness of Type Ia Supernovae for Cosmology - a Personal Review
  We review some results of the past 12 years derived from optical and infrared
photometry of Type Ia supernovae. A combination of optical and infrared
photometry allows us to determine accurately the extinction along the line of
sight. The resulting distance measurements are much more accurate than can be
obtained from optical data alone. Type Ia supernovae are very nearly standard
candles in the near-infrared. Accurate supernova distances, coupled with other
observational data available at present, allow us to determine the matter
density in the universe and lead to evidence for the existence of Dark Energy.
We can now address some questions on the grandest scale such as, "What is the
ultimate Fate of the universe?"
