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).