The advent of enzyme immobilization, allowing re-use of enzymes, and essentially eliminating product contamination, has greatly increased the potential of enzymatic processes for industrial use. Although this is a relatively new field of study, the literature is rapidly expanding. The compendium of references prepared by the New England Research Applications Center for Corning Glass Works now lists over 800 papers concerning immobilized enzymes. For this reason the scope of this paper is limited to immobilized enzyme engineering, including reactor design and performance. Although medical and analytical applications of immobilized enzymes are important, they will not be discussed as such here. Another large body of information concerning enzyme immobilization techniques will be treated only briefly as an introduction. Other general articles and reviews [1–5] may be useful in providing additional background information.