In this book, an ensemble of examples is provided to illustrate the diversity of approaches and applications to which the multi-enzyme catalysis is currently applied. Enzymes act in living beings as extremely complex, network mixtures that are supportive of all the biochemical transformations on which the life is based. In the biotechnological context, many of the enzymatic processes performed in vitro at both small and industrial scales lie on the enzymatic transformation of a single molecular species for the generation of a product and as catalyzed by a single enzyme. However, the number of technological applications for which cell-free enzyme mixtures are required is increasing and the science of how to combine individual reactions in complex processes is under speedy development. Obviously, any of the current in-progress multi-enzyme processes is fully mimicking the complexity of a living cell or cell community. However, the refined combination of selected enzymes and substrates is offering a new technological approach that is supporting the development of new or improved products in many fields such as food, leather and pharmaceutical industries. This book is unique and presents selective examples of each of these processes have been incorporated in this book by experts in their respective areas.