Most industrial enzymes (biocatalysts) can be obtained from microorganisms. The advantages of using microorganisms are numerous. Plants and animals grow slowly in comparison with microorganisms, enzymes form only small portions of the total plant or animal; and large tracts of land and huge numbers of animals would be necessary for substantial productions. These limitations make plant and animal enzymes expensive. Microbial enzymes on the other hand are not subject to the above constraints. By far, the greatest attraction for the production of microbial enzymes is the great diversity of enzymes which reflects the diversity of microbial types in nature. Thus, due to the widely varying environmental conditions in nature, microbial enzymes have been isolated which are able to operate under extreme environmental conditions. Immobilization of enzymes and cells provides a basis for the re-use of enzymes and cells. This chapter discusses enzymes produced by microorganisms, uses of enzymes in the industry, production of enzymes, fermentation for enzyme production, enzyme extraction, packaging and finishing, toxicity testing and standardization, immobilized enzymes and cells, general advantages of immobilized biocatalysts, methods of immobilizing enzymes, methods for the immobilization of cells, and application of immobilized biological catalyst systems.