During the last decade our expertise in nanotechnology has advanced considerably. The possibility of incorporating in the same nanostructure different organic and inorganic materials has opened up a promising field of research, and has greatly increased the interest in the study of properties of excitations in organic materials. In this book not only the fundamentals of Frenkel exciton and polariton theory are described, but also the electronic excitations and electronic energy transfers in quantum wells, quantum wires and quantum dots, at surfaces, at interfaces, in thin films, in multilayers, and in microcavities. Among the new topics in the book are those devoted to the optics of hybrid Frenkel-Wannier-Mott excitons in nanostructures, polaritons in organic microcavities including hybrid organic-inorganic microcavities, new concepts for organic light emitting devices, the mixing of Frenkel and charge-transfer excitons in organic quasi one-dimensional crystals, excitons and polaritons in one and two-dimensional crystals, surface electronic excitations, optical biphonons, and Fermi resonances by polaritons. All new phenomena described in the book are illustrated by available experimental observations. The book will be useful for scientists working in the field of photophysics and photochemistry of organic solids (for example, organic light-emitting devices and solar cells), and for students who are entering this field. It is partly based on a book by the author written in 1968 - "Theory of Excitons" - in Russian. However the new book includes only 5 chapters from this version, all of which have been updated. The 10 new chapters contain discussions of new phenomena, their theory and their experimental observations.

The Advanced Study Institute on 'Elementary Excitations in Solids, Molecules, and Atoms' was held at the University of Antwerp (U.I.A.) from June 18th till June 30th 1973. The In stitute was sponsored by NATO. Co-sponsors were: Agfa-Gevaert N.V. (Mortsel-Belgium), Bell Telephone Mfg. Co. (Antwerp-Belgium), I.B.M. BelgiumN. V. (Brussels-Belgium), the National Science Founda tion (Washington D.C. - U.S .A.) and the Uni versi ty of Antwerp (U.I .A.) . A total of 120 lecturers and participants attended the Institute. Over the last few years, substantial progress has been made in the description of the elementary excitations of the elec tronic and vibrational systems and their interactions. Parallel with this, the experimentalists have obtained outstanding re sults, partly as a result of availability of coherent light sour ces from the far infrared through the visible region, and partly because of the availability of synchrotron radiation sources in the soft X-ray region. The results of today will lead to fur ther progress over the next years. It was the purpose of this NATO Advanced Study Institute to present a state of the art, namely a survey of experiment and theory.

The Advanced Study Institute on 'Elementary Excitations in Solids, Molecules, and Atoms' was held at the University of Antwerp (U.I.A.) from June 18th till June 30th 1973. The In stitute was sponsored by NATO. Co-sponsors were: Agfa-Gevaert N.V. (Mortsel - Belgium), Bell Telephone Mfg. Co. (Antwerp Belgium), the National Science Foundation (Washington D.C. - U.S.A.) and the University of Antwerp (U.I.A.). A total of 120 lecturers and participants attended the Institute. Over the last few years, substantial progress has been made in the description of the elementary excitations of the elec tronic and vibrational systems and their interactions. Parallel with this, the experimentalists have obtained outstanding re sults, partly as a result of availability of coherent light sour ces from the far infrared through the visible region, and partly because of the availability of synchrotron radiation sources in the soft X-ray region. The results of today will lead to fur ther progress over the next years. It was the purpose of this NATO Advanced Study Institute to present astate of the art, namely a survey of experiment and theory.

This text continues to fill the need to communicate the present view of a solid as a system of interacting particles which, under suitable circumstances, behaves like a collection of nearly independent elementary excitations. In addition to introducing basic concepts, the author frequently refers to experimental data. Usually, both the basic theory and the applications discussed deal with the behavior of '`'simple' metals, rather than the '`'complicated' metals, such as the transition metals and the rare earths. Problems have been included for most of the chapters.