This volume contains all of the invited lectures presented at the NATO ARWon New Methods in Quantum Theory held in Halkidiki, Greece from May 14th to May 19th, 1995. This survey of new perspectives, techniques and results in quantum theory contains 26 chapters by leading quantum chemists and physicists from 14 countries. The book covers a wide range of topics, though the emphasis throughout is on new approaches and their interrelationships. Topics covered include dimensional scaling, the hyperspherical method applied both to reactive scattering theory and to bound state problems, chaotic behaviour, large-order perturbation theory, complex eigenvalues and quasistationary states, semiclassical methods, cusps in hyperaccurate wave functions, density functional theory, relativistic quantum theory, and quantum Monte Carlo methods. I hope very much that the various lectures presented at this Advanced Research Workshop will be of as great interest to the reader as they were to the participants. The organization of the ARW would have been impossible without the generous funding by NATO, which is gratefully acknowledged. I sincerely thank Drs. J. -M. Cadiou, Assistant Secretary General for Scientific and Environmental Affairs, and J. A. Rausell-Colom, Programme Director for Priority Area on High Technology, North Atlantic Treaty Organization, who helped me throughout the various stages of the ARW.