I/Methods of Quantum Chemistry.- The History of the X? Method.- Configuration Interaction Description of Electron Correlation.- Some Problems of the Theory of Intermolecular Interactions.- II/Electronic Structure and Conformation of Molecules.- Remarks on Calculations of Molecular Electronic Structure.- Molecular Orbital Theory of the Conformation of Small Organic Molecules.- Conformational Studies in Quantum Biochemistry.- III/General Theory of Chemical Reactivity.- to Symposium III: General Theory of Chemical Reactivity.- Quantum Mechanics of Simple Chemical Reactions.- The Charge and Spin Transfers in Chemical Reaction Paths.- IV/Formation and Evolution of Molecular Excited States.- Preparation and Decay of Excited Molecular States.- Some Aspects of UPS.- V/Effects of Environment on the Behaviour of Molecules.- Introductory Remarks.- Intermolecular Forces and the Electric and Magnetic Properties of Molecules.- Three Types of Potential Needed in Predicting Conformations of Molecules in Solution and Their Use.- Molecular interactions in Ground and Excited States.