This book covers the topics of the existence of planets around others stars. We think now we are unique in the Universe, but the Universe is very large. This book just touches the surface of this very exciting field. With better telescopes and data processing methods, more planets in our galaxy have been found. Dedicated planet-finding facilities on the ground and in space have been deployed. We now see that planets are rather common in our galaxy. The next big question is, do any of them have life?