Extraterrestrial life is a common theme inscience fiction, but is it a serious prospect in the real world? Astrobiologyis the emerging field of science that seeks to answer this question.The possibility of life elsewhere in the cosmosis one of the most profound subjects that human beings can ponder. AstrophysicistAndrew May gives an expert overview of our current state of knowledge, lookingat how life started on Earth, the tell-tale ''signatures'' it produces, and howsuch signatures might be detected elsewhere in the Solar System or on the many ''exoplanets''now being discovered by the Kepler and TESS missions.Along the way the book addresses key questions such as the riddle of Fermi''sparadox (''Where is everybody?'') and the crucial role of DNA and water - they''reessential to ''life as we know it'', but is the same true of alien life? And the reallybig question: when we eventually find extraterrestrials, will they be friendlyor hostile?