Are we alone in the universe?  Answers to this fundamental question have been offered for millenia from widely differing philosophical and religious perspectives. But only in modern times has an attempt been made to study it scientifically. Although we have as yet only a very partial understanding, we can begin to study how everything from big bang cosmology to the discovery of extra-solar planets, from stellar astronomy to planetary geology, and from cellular DNA to the SETI project may contribute to its answer.