Enzymes perform the executive role in growth, energy conversion, and repair of a living organism. Their activity is adjusted to their environment within the cell, being turned off, switched on, or finely tuned by specific metabolites according to demands at the physiologi­ cal level. Each enzyme discovered in the long history of enzymology has revealed its own individuality. Even closely related members of a family differ in specificity, stability or regulatory properties. Despite these, at first sight overwhelming aspects of individuality, common factors of enzymic reactions have been recognized. Enzymes are stereospecific catalysts even when a nonspecific process would yield the same product. Knowledge of the detailed stereochemistry of an enzymic reaction helps to deduce reaction mechanisms and to ob­ tain insight into the specific binding of substrates at the active site. This binding close to catalytically competent groups is related to the enormous speed of enzyme-catalyzed reactions. The physical ba­ sis of rate-enhancement is understood in principle and further exploit­ ed in the design of small organic receptor molecules as model enzymes. These aspects of enzyme catalysis are discussed in Session 1. Session 2 emphasizes the dynamic aspects of enzyme substrate inter­ action. Substrate must diffuse from solution space to the enzyme's surface. This process is influenced and can be greatly facilitated by certain electrostatic propterties of enzymes. The dynamic events during catalysis are studied by relaxation kinetics or NMR techniques.