This book explores the science of extraterrestrial life, with a particular emphasis on the existence of intelligent alien civilizations. It introduces the reader to the basic chemistry associated with life on Earth and describes the planetary and stellar environments that allow us to exist. It also discusses the likelihood of alien life developing at other locations in our galaxy, along with the possibility that we will meet or communicate with them. This book is suitable for use as a text in an introductory "Life in the Universe" course.