Microscopic Many-Body theory of strongly interacting quantum systems such as helium liquids, liquid mixtures, electrons, and selected nuclear problems. Special focus of the past years was the study of surface effects and other properties of quantum liquids in confined geometries such as adsorbed films, clusters, and other quasi-two- dimensional structures Analysis of neutron and atom scattering experiments quantum from quantum liquids, surface phonon and plasmon dispersion. Fermi-Liquid theory, dynamics, and thermodynamics of quantum liquids and quantum liquid mixtures. Numerical methods for density functional theory, especially real-space algorithms and their application to metal clusters.