Today we know of only a single planet that hosts life: the Earth. But across a Universe of at least 100 billion possibly habitable worlds, surely our planet isn't the only one that, like the porridge Goldilocks sought, is just right for life? Astrobiologists search the galaxy for conditions that are suitable for life to exist, focusing on similar worlds located at the perfect distance from their Sun, within the aptly named 'Goldilocks Zone'. Such a place might have liquid water on its surface, and may therefore support a thriving biosphere. What might life look like on other worlds? It is possible to make best-guesses using facts rooted in science, and by studying 'extremophiles' – organisms such as the near-indestructible water bears, which can survive in the harshest conditions that Earth, and even space, can offer. Goldilocks and the Water Bears is a tale of the origins and evolution of life, and the quest to find it on other planets, on moons, in other galaxies, and throughout the Universe.