In Searching for Water in the Solar System, Thérèse Encrenaz takes the reader on a journey through the Universe in search of water. She begins by introducing the most well-known of molecule H2O, its physical and chemical characteristics and its cosmic Formation and abundance. She examines the methods by which the presence of water is detected, both within the solar system and beyond. One by one she visits a diversity of locations in the cosmos, from the nearest planets to the furthest galaxies, where water has been discovered. In the formation of the solar system, she explains how the water molecule played a major part, with the so-called ‘ice frontier’ determining the natures of the terrestrial and giant planets. The book explores the presence of water in the various bodies of the Solar System: in the giant planets, with their rings and systems of satellites, in comets, asteroids and in the terrestrial planets. By tracing the history of water in the atmospheres of Mars, Venus and the Earth, the author explains how small differences in temperatures, causing water to exist in different states on different planets – vapour on Venus, liquid on Earth and solid ice on Mars – have led to a great divergence in the evolutions of the three planets. The story of water on Mars, an aspect of great topical interest, offers an insight into the possibility (still only a theory) that there was once life on that planet. The book concludes by looking at the important role played by water in studies of habitable exoplanets.