We present an overview of new procedures for including quantummechanical effects in enzyme kinetics. Quantum effects areincluded in three ways: (1) The electronic structure of the atomsin the catalytic center is treated quantum mechanically in orderto calculate a realistic potential energy surface for the bondrearrangement process. (2) The discrete nature of quantum mechanical vibrational energies is incorporated in the treatment ofnuclear motion for computing the potential of mean force. (3)Multidimensional tunneling contributions are included. Theseprocedures are illustrated by applications to proton abstractionscatalyzed by enolase and methylamine dehydrogenase and hydride-transfer reactions by alcohol dehydrogenase and xylose isomerase.