Molecular interactions : concepts and methods Chapters in this book begin with coverage of the concepts and methods for simpler systems then move on to more advanced subjects for complex systems. Each chapter begins with qualitative aspects before these are treated in quantitative fashion. The first four chapters include the established concepts and quantitative aspects of long range (electrostatic induction and dispersion) forces and how they extend to intermediate and short ranges for ground and excited states. They are followed by chapters dealing with recent developments including electronically non adiabatic interactions correlated many electron treatments generalized density functional theory decomposition and embedding of molecular fragments for large systems and very recent developments using artificial intelligence with network training for many atom systems