We have now reached an exciting time in cometary research. With several missions launched or about to be launched in the near future, cometary research is rapidly being driven forward. This book describes the wealth of information known prior to the return of Halley’s comet, and the new information discovered since then. It presents material on important background topics including observational techniques, plasma physics, celestial mechanics, the solar wind and cosmogony. The science of comets is described in order of its discovery, from tail phenomena to coma morphology through to the most recent findings from space missions. The relationship between comets and asteroids is discussed, and future space missions to investigate comets are described. This comprehensive text is a complete and up-to-date treatment of the subject, suitable for graduate and advanced undergraduate students of astronomy and planetary science.