Preface.- Introduction.- Hierarchy of Terms in the Effective Hamiltonian.- Spectroscopic Perturbations: Homogeneous and Heterogeneous.- The Effective Hamiltonian for Diatomic Molecules.- Rotation of Polyatomic Molecules.- Quantum Beats.- The Effective Hamiltonian for Polyatomic Molecule Vibration.- Intramolecular Dynamics: Representations, Visualizations and Mechanisms.