This document summarizes enzymes and their functions. It defines enzymes as biological catalysts that accelerate chemical reactions and lower activation energy. Most enzymes are proteins that achieve catalytic effects through their 3D structure. The molecules enzymes act upon are called substrates. The enzyme binds to the substrate to form an enzyme-substrate complex, upon which the substrate is converted to product and released. Enzymes are very specific and can accelerate reactions millions of times. They are not consumed in reactions and can be reused. Enzymes have many industrial applications including food processing, brewing, paper-making, and dairy production.