This splendid book explains both the triumph and the mystery that is quantum theory. It is a triumph because of its towering mathematical structure, and amazing empirical accuracy. It is a mystery because of the conundrums about how to interpret it. John Polkinghorne, himself a distinguished quantum physicist, is a sure guide to all of this: he celebrates the successes of the theory, and shows unfailingly good judgement about the conundrums. * Jeremy Butterfield, University of Oxford * John Polkinghorne has produced an excellent piece of work. ... Many authors of popular books on modern physics have the regrettable habit of mixing science fact with science fiction. Polkinghorne never does that: he always allows the truth to stand by itself and show its own fascination. ... I think that this is an excellent contribution to the literature on quantum theory for a general audience. * Chris Isham, Imperial College, London * John Polkinghorne has brought to life that most mysterious and perplexing of revolutions in understanding and has made its mysteries accessible. * Peter Atkins, University of Oxford *