The study of planetary systems, many unlike the Solar System, challenge some aspects of scientists’ understanding of planet formation. Yet one message conveyed by these discoveries is clear: the formation of planets frequently, startand perhaps always, accompanies the formation of stars. The implications of this conclusion are profound. Planets are a common by-product of star formation. In a galaxy of 200 billion stars, and a universe of hundreds of billions of galaxies, how many planets (or even moons) might exist? And with all of these planets in the universe, how many might have suitable conditions for the particular category of chemical reactions that we refer to as “life”?