Discovering Pluto is an authoritative account of the exploration of Pluto and its moons, from the first inklings of tentative knowledge through the exciting discoveries made during the flyby of the NASA research spacecraft New Horizons in July 2015. Co-author Dale P. Cruikshank was co-investigator on the New Horizons mission, while co-author William Sheehan is a noted historian of the solar system. Telling the tale of Pluto’s discovery, the authors recount the grand story of our unfolding knowledge of the outer solar system, from William Herschel’s serendipitous discovery of Uranus in 1781, to the mathematical prediction in 1846 of Neptune’s existence, to Percival Lowell’s studies of the wayward motions of those giant planets leading to his prediction of another world farther out. Lowell’s efforts led to Clyde Tombaugh’s heroic search and discovery of Pluto—then a mere speck in the telescope—at Lowell Observatory in 1930. Pluto was finally recognized as the premier body in the Kuiper Belt, the so-called third zone of our solar system. The first zone contains the terrestrial planets (Mercury through Mars) and the asteroid belt; the second, the gas-giant planets Jupiter through Neptune. The third zone, holding Pluto and the rest of the Kuiper Belt, is the largest and most populous region of the solar system. Now well beyond Pluto, New Horizons will continue to wend its lonely way through the galaxy, but it is still transmitting data, even today. Its ultimate legacy may be to inspire future generations to uncover more secrets of Pluto, the solar system, and the universe.