This inaugural volume in a new series on quantum many-body theory contains the papers presented at the Ninth International Conference on Recent Progress in Many-Body Theories. The conference focused on the development and refinement of many-body methods. A major aim was to foster the exchange of ideas among physicists working in such diverse areas as nuclear physics, quantum chemistry, complex systems, lattice Hamiltonians, quantum fluids and condensed matter physics. A special feature was a session devoted to theories for many-electron systems in low-dimensional quantum dots, wires and...