An update of a comprehensive text, which covers all the important aspects of modern molecular electronic-structure theory providing in-depth background material. It derives in detail important working equations of computational electronic-structure theory that readers are able to use to write a computer program. All of the existing chapters have been thoroughly updated and four new chapters have been added: * Provides a comprehensive, up-to-date, and technical monograph on this subject. * Makes extensive use of numerical examples. * Methods are supported by actual examples and not merely model calculations. * Problems and exercises are provided at the end of each chapter, complete with hints and solutions. * The new edition will include four new chapters on: The electronic Hamiltonian; Time-independent response theory; Time-dependent response theory & Density-functional theory (DFT)