In this chapter, a summary of issues regarding enzymes in ionic liquids has been provided. In general, most of enzymes can be used in adequate ionic liquids. In most cases, it is found that ionic liquids with hydrophobic nature, less viscosity, kosmotropic anion and chaotropic cation usually enhance the activity and stability of enzymes. The activity and stability of enzyme in ionic liquids can be improved by immobilization, modification with activated stabilizing agents, pretreatment with polar organic solvents or by reaction media engineering such as mircroemulsion, using co-solvent, and design of biocompatible ionic liquids, etc. Furthermore, the information regarding structure and conformation dynamics of protein in ionic liquids could be helpful for engineering and scientific communities
to understand how ionic liquids enhance the stability and activity of enzymes, and thereafter be useful for choosing or designing ionic liquids for specific enzymatic reactions with the help of quantum chemistry.