The Concept of Molecular Structure.- Topology and Properties of Molecules.- Symmetry in Molecules.- Chirality of Molecular Structures - Basic Principles and Their Consequences.- Interplay of Experiment and Theory in Determining Molecular Geometries. A. The Experiments.- Interplay of Experiment and Theory in Determining Molecular Geometries. B. Theoretical Methods.- Molecular Mechanics alias Mass Points and Elastic Springs Model of Molecules.- Atoms in Molecular Evironments.- The Modelling of Molecules as Collections of Modified Atoms.