For five decades after its discovery in 1930, the planet Pluto remained an enigma. However, several events during the last two decades have helped to lift the veil of mystery surrounding the ninth planet. The discovery of its satellite, Charon, in 1978 permitted occultation observations that allowed scientists to determine the size of both bodies. Astronomers also detected the presence of an atmosphere, and the Hubble Space Telescope provided views in unprecedented detail. In addition to these two fortuitous events, advances in telescopic instrumentation and computational methods led to exciting observational and theoretical discoveries. This new Space Sciences Series volume focuses on the scientific issues associated with Pluto and Charon. Fifty collaborating authors here review the latest research on the Pluto-Charon binary, from bulk properties, surfaces and interiors to atmospheric structure, composition, and dynamics. They also provide historical perspectives on Pluto-Charon research and discuss the population of the trans-Neptunian region and the origin of the Pluto-Charon binary. Also included are prefatory remarks by Pluto's and Charon's discoverers, Clyde Tombaugh and James Christy. This volume offers the most comprehensive available compendium of research work for understanding these far off members of our solar system, just at a time following dramatic developments in our knowledge but before that knowledge can be advanced by spacecraft missions.