Other Worlds NASA's Kepler Mission is determining the frequency of habitable, Earth-like planets in the universe. Kepler detects Earth-like planets by searching for the tiny dimming in brightness of the planet's host star when the planet's orbit takes it in front of the star, as seen by Kepler. Kepler is a 95-cm-diameter space telescope that is staring at over 150,000 stars in the constellations of Cygnus and Lyra, waiting for the multiple, periodic transits that indicate a planet is in orbit. Kepler was launched in March 2009 and by February 2011 will have been taking data for nearly 2 years, long enough to begin to assess the frequency of Earth-size planets on year-long orbits around solar-type stars. Based on ground-based planet searches by other techniques, the expectation is that Kepler will discover large numbers of super-earths -- planets with masses up to about 15 times that of Earth, which appear to accompany roughly one-third of all solar-type stars. Kepler should then discover dozens of Earth-like planets, that is, planets of Earth-size orbiting in the habitable zones of their stars. Kepler will also make an extraordinary contribution to our understanding of stellar structure and evolution, as the same high photometric precision needed to detect earth also means that stellar brightness variations will be measured to unprecedented accuracies over the 3.5-year mission lifetime, permitting seismological studies of stellar interiors and new insights into variable stars.