Advances in the physics and chemistry of low-dimensional systems have been really magnificent in the last few decades. Hundreds of quasi-one-dimensional and quasi-two-dimensional systems have been synthesized and studied. The most popular representatives of quasi-one-dimensional materials are polyacethylenes CH [1] and conducting donor-acceptor molecular crystals TIF z TCNQ. Examples of quasi-two-dimensional systems are high temperature su perconductors (HTSC) based on copper oxides LA2CU04, YBa2Cu306+y and organic superconductors based on BEDT -TIP molecules. The properties of such one- and two-dimensional materials are not yet fully understood. On the one hand, the equations of motion of one-dimensional sys tems are rather simple, which facilitates rigorous solutions of model problems. On the other hand, manifestations of various interactions in one-dimensional systems are rather peculiar. This refers, in particular, to electron--electron and electron-phonon interactions. Even within the limit of a weak coupling con stant electron--electron correlations produce an energy gap in the spectrum of one-dimensional metals implying a Mott transition from metal to semiconductor state. In all these cases perturbation theory is inapplicable. Which is one of the main difficulties on the way towards a comprehensive theory of quasi-one-dimensional systems. - This meeting held at the Institute for Theoretical Physics in Kiev May 15-18 1990 was devoted to related problems. The papers selected for this volume are grouped into three sections. This volume presents lectures on new approaches to electron-electron and electron-phonon correlation effects in low-dimensional materials: organic solids, conducting polymers such as polyacetylenes (CH)x, organic and copper-oxide superconductors with high Tc values. Key points: correlation effects in optical spectra, magnetic properties, nonlinear processes, electrons in 1-d and 2-d solids and their molecular components, new approaches to 1-d and 2-d Hubbard models, Peierls model, multi-configurational approach to large systems, calculation of Madelung energy in complex crystals, quantum field model, kink effects in optical spectra of high Tc superconductors. Researchers in the fields of solid state physics and superconductivity will find this collection of papers particularly useful. Die Beiträge in diesem Band befassen sich mit neuen Zugängen zur Elektron-Elektron- und Elektron-Phonon-Wechselwirkung in niedrig-dimensionalen Systemen: organischen Festkörpern, leitenden Polymeren wie Polyacethylenen (CH)x, organischen Supraleitern und Kupferoxydsupraleitern mit hohen Tc-Werten. Die hier gesammelten Aufsätze sind für all jene ganz besonders interessant, die in der Festkörperphysik und auf dem Gebiet der Supraleitung forschen.