This chapter contains sections titled: Diffusion Interaction between Macromolecules and Ligands Binding Constants Macromolecules with One Binding Site Macromolecules with Identical Independent Binding Sites General Binding Equation Graphic Representations of the Binding Equation Direct and Linear Diagrams Analysis of Binding Data from Spectroscopic Titrations Binding of Different Ligands, Competition Non-competitive Binding Macromolecules with Non-identical, Independent Binding Sites Macromolecules with Identical, Interacting Binding Sites, Cooperativity The Hill Equation The Adair Equation The Pauling Model Allosteric Enzymes The Symmetry or Concerted Model The Sequential Model and Negative Cooperativity Analysis of Cooperativity Physiological Aspects of Cooperativity Examples of Allosteric Enzymes Hemoglobin Aspartate Transcarbamoylase Aspartokinase Phosphofructokinase Allosteric Regulation of the Glycogen Metabolism Membrane Bound Enzymes and Receptors Non-identical, Interacting Binding Sites References