Astrobiology is an exciting new subject, and one, arguably, more interdisciplinary than any other. Astrobiologists seek to understand the origin and evolution of life on Earth in order to illuminate and guide the search for life on other planets. In this Very Short Introduction, David C. Catling introduces the subject through our understanding of the factors that allowed life to arise and persist on our own planet, and for the signs we are looking for in the search for extraterrestrial life.