Quantum theory is one of the more abstract branches of theoretical physics, yet it makes clear and concrete predictions which are repeatedly verified experimentally. More recently, there has been some confluence between the concepts of microphysics and those of macrophysics. Currently fashionable ideas in cosmology are also deeply linked to concepts from quantum theory, thus piquing greater interest in this subject. This timely book takes stock of what quantum theory has achieved and where it is leading to at present, in a manner understandable to an educated layman.The book describes concepts in a strictly scientific manner without trying to make them sound overly philosophical or “hyping” them up. At the same time, careful explanation of the concepts and details (including the technical terminology) are given in a nonmathematical language for the general reader. In particular, emphasis is given to the specific aspects of quantum theory that interface with gravity and cosmology, so as to keep the book reasonably up to date and focused on a key underlying theme.