Are we alone in the Universe? Or are there myriads of other habitable worlds teeming with life and intelligence? These are questions of long standing, going back at least to the ancient Greeks, e.g. Epicurus (341–270 BC) who opined: ‘There are infinite worlds similar to and different from our own’. Until the end of the twentieth century, however, all was speculation because the necessary observational techniques did not exist. It is only very recently, in the last decade, that the situation has started to change. Although we still cannot answer the questions about life, there has been an avalanche of evidence pointing to the existence of exoplanets, i.e. extra-solar planets in orbits around other stars. The authors have set out to provide a detailed snapshot of this rapidly developing research field at a particularly exciting moment in its evolution.