The term “immobilized enzymes” refers to “enzymes physically confined or localized in a certain defined region of space with retention of their catalytic activities, and which can be used repeatedly and continuously.”. Besides the application in industrial processes, the immobilization techniques are the basis for making a number of biotechnological products with applications in diagnostics, bioaffinity chromatography, and biosensors. Initially, only immobilized single enzymes were used, but the 1970s saw the development of more complex systems—including two-enzyme reactions with co-factor regeneration and living cells. The major components of an immobilized enzyme system are the enzyme, the matrix, and the mode of attachment. The enzymes can be attached to the support by interactions ranging from reversible physical adsorption and ionic linkages to stable covalent bonds. The covalent reactions commonly employed give rise to binding through amide, ether, thio-ether, or carbamate bonds. As a consequence of enzyme immobilization, some properties such as catalytic activity or thermal stability become altered. These effects have been demonstrated and exploited. The concept of stabilization has been an important driving force for immobilizing enzymes. True stabilization at the molecular level has been demonstrated (e.g., proteins immobilized through multipoint covalent binding).