Written by expert researchers, this book covers all the major aspects of research in Jupiter's moon Io, from the interior to its space environment. Io is one of the Solar System’s most exotic satellites. The book discusses Io's interior, geology, atmosphere, and, in particular, its active volcanism, which was discovered from observations by the Voyager 1 spacecraft in 1979, confirming a possibility suggested from theoretical studies based on Io’s orbit. Our knowledge of Io’s volcanism, composition, and space environment was significantly increased as a result of observations by other spacecrafts, including Galileo. More than a decade after the 1st edition, “Io After Galileo”, this 2nd edition of the book now includes results obtained by the New Horizons mission and, more recently, Juno. It also presents observational results from ground-based telescopes using adaptive optics having provided resolutions that rival those of spacecraft. The book provides a review of the current status of Io research and gives an outlook to planned future observations. It thus serves as reference for researchers in the field and an introduction for PhD students and newcomers planning to study this exotic Solar System moon.