Introduction.- Principles and Techniques.- Experiments.- Water Monomer: Structure and Diffusion of a Single Water Molecule.- Water Dimer: Direct Observation of Hydrogen-Bond Exchange.- Water Clusters: Formation of One-Dimensional Water Clusters.- Hydroxyl Group: Tunneling Dynamics of Hydrogen Atom.- Hydroxyl Dimer: Non-linear I-V Characteristics in an STM Junction.- Water-Hydroxyl Complexes: Direct Observation of a Symmetric Hydrogen Bond.- One-Dimensional...