The book will contain about 20 selected contributions based on presentations given at the 15th International Workshop on Quantum Systems in Chemistry and Physics, to be held at Cambridge, England, in September 2010 (see http://qscp-xv.ensicaen.fr/). The book will be divided into a few sections, each containing the most relevant papers written by leaders of the respective fields on related topics. They will discuss state-of-the-art developments in the Theory of Quantum Systems in Chemistry and Physics. This is a book of proceedings and its contents will depend on the scientists who will attend the meeting and provide research or review papers accepted for publication. A provisional list of speakers can be found on the workshop web site: http://qscp-xv. ensicaen.fr/index.php. The detailed table of contents will be provided at a later date.