This book compiles detailed information concerning a dozen of the best known allosteric enzymes, and so allows the comparison of their regulatory mechanisms and the confrontation of these mechanisms with the theoretical models. Stimulating and unexpected ideas emerge from these comparisons and emphasize the importance of developing various methods of investigation such as crystallography, X-ray solution scattering, and the study of fast movements in proteins and site-directed mutagenesis. This book is addressed to students and researchers interested in structure-function relationship in proteins, enzymology and metabolic regulation. It is also a basis for teaching.