Whether we are alone in the Universe is a question that has fascinated humans since the earliest of times. Today the search for extraterrestrial life focuses on understanding how life arose on Earth to investigate the potential for life elsewhere. Beginning with the Big Bang and formation of the Universe, this text investigates the emergence of life on Earth, describing the factors and key stages necessary for the development of microorganisms. It then considers the possibility of life arising under similar conditions on other planets. From the deepest depths of the ocean floor to the outmost edges of the galaxy, the potential for life is explored. Mars, Europa - the water-rich satellite of Jupiter - and Saturn's enigmatic moon, Titan are investigated as ideal candidates for exploration. Beyond the solar system, the search for Earth-like planets is also considered.