Ligand-macromolecule interactions are of fundamental importance in the control of biological processes. This book applies the principles of linkage thermodynamics to polyfunctional macromolecular systems under equilibrium conditions, and describes the binding, linkage, and feedback phenomena that lead to control of complex metabolic processes. The first chapter sets out the different processes (conformational changes, changes in state of aggregation, phase changes) involving biological macromolecules which are affected by chemical variables (such as ligands) or physical variables (such as temperature and pressure). The general effects of ligands on micromolecular conformations and interactions are illustrated with specific examples from the respiratory proteins, electron-transport proteins, and nucleic acid binding proteins. Subsequent chapters develop these themes, and describe in detail how the mathematics of regulation and control can be applied to macromolecules in biological system. This book should be of interest to all those using thermodynamics to understand the physical chemical basis of control of life processes. It is designed for graduate students and researchers in biophysical chemistry.