These two volumes collect forty-four selected papers from the scientific contributions presented at the Third European Workshop on Quantum Systems in Chemistry and Physics, held in Granada (Spain), April 19-22, 1998. Ninety-nine scientists from Bulgaria, Columbia, Cuba, Denmark, Finland, France, Germany, Hungary, Israel, Italy, Mexico, Netherlands, Norway, Poland, Russia, Slovakia, Spain, Sweden, United Ki- dom, Uruguay and Venezuela attended the workshop, discussing the state of the art, new trends, and future evolution of the methods and applications. The workshop took place at the 'Los Alixares' Hotel, where 45 lectures were given by prominent members of the scientific community; in addition, 49 posters were presented in two very animated sessions. The success of this workshop is due, without doubt, to the excellent tradition initiated at the previous workshops, organised by Prof. R. McWeeny in San Miniato, Pisa (Italy), 1996, and by Prof. S. Wilson in Oxford (United Kingdom), 1997. These workshops create occasions for meetings and disc- sions on the current state of the art, emerging methods and applications and new trends in this area of science. The three meetings were sponsored and partially supported by the European Union (EU) in the frame of the Cooperation in Science and Technology (COST) chemistry actions.

These two volumes together comprise forty papers coming from the most outstanding contributions to the third European Quantum Systems in Chemistry and Physics Workshop held in Granada, Spain (1997). These books cover a very broad spectrum of scientific research work from quantum-mechanical many-body methods to important applications and computational developments, and from atoms and molecules to condensed matter. The first volume is subtitled Basic Problems and Model Systems, and includes the following topics: density matrices and density functionals, electron correlation effects, relativistic formulations, valence theory, and nuclear motions. The second volume is subtitled Advanced Problems and Complex Systems and covers the following topics: response theory, condensed matter, reactive collisions and chemical reactions, and computational chemistry and physics.