Overview of Protein Structural Elements and Basic Definitions Non-covalent Interactions and Structure-Function Relationships in Proteins Observation of van der Waals Interactions Nature of van der Waals Interactions Potential Functions for Application in Proteins Approximation for Polyatomic Systems Nature of Hydrogen Bonds Geometry and Strength of the Hydrogen Bond Hydrogen Bonds in Proteins Hydrogen Bonds and Protein Stability Nature of Hydrophobic Interactions, Pseudo Forces Water Hydrophobic Effect Hydrophobic Interactions in Proteins Debye-Huckel Theory Ion-Solvent Interactions Calculation of Electrostatic Interactions in Proteins Why Does One Need to Know Ionization Equilibria? Factors Determining Ionization Equilibria in Proteins Combinatorial Problem Cooperative Ionization Allocation Variation of Polar Hydrogen Atoms Examples for pH-Dependent Hydrogen Bonding Conformational Flexibility Involving Non-Hydrogen Atoms Unfolding Induced by pH Modeling of Unfolded Proteins Thermal Stability of Proteins.