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 concept