Quantum theory is one of the most important and successful theories of modern physical science. It has been estimated that its principles form the basis for about 30 per cent of the world's manufacturing economy. This is all the more remarkable because quantum theory is a theory that nobody understands. Baggott brings the reader up to date with the results of experimental tests of quantum non-locality and complementarity that have been successfully he also reviews the latest thinking on alternative interpretations - pilot waves, decoherence, consciousness, many worlds and God - and the frontiers of quantum cosmology, quantum gravity and potential applications of quantum entanglement in computing, cryptography and teleportation. Quantum theory emerges largely unscathed, only serving to reinforce the point that the theory remains the most powerful framework for explaining observations of the quantum world, but that its orthodox interpretation continues to offer little in the way of understanding in terms of underlying physical processes. Quantum theory remains a mysterious theoretical black top hat from which white rabbits continue to be pulled. Students are usually advised not to ask how this particular conjuring trick is done.