Humans have long wondered what other planetary systems are like, and if potentially Earth-like planets exist around other stars. NASA's Kepler Mission is a space telescope that was designed to answer these questions. From four years of Kepler data we can now confidently say that the average planetary system looks nothing like our own. Nature often makes compact planetary systems where several planets orbit closer in that Mercury's distance, where our planetary system is entirely empty. Within the startling diversity in planetary systems, Kepler data can be combed to understand how common Earth-size planets really are. I will discuss a variety of recent estimates that all point to tens of billions of Earth-sized planets in our Milky Way, and discuss the fraction of these that may be temperate enough to potentially support life.