Alien worlds orbiting other stars were the subject of speculation going back to ancient times, and were finally discovered in the 1990’s. Thousands of extrasolar planets, and hundreds of multiple-planet systems, are now known and show a remarkable variety compared to our own solar system. This course discusses the known exoplanets: how they are discovered, their orbits and physical properties. The theoretical understanding of planet formation and evolution will be used to understand the known planets, how they likely formed and their ultimate fate.