5,000 Years ago, people stored milk in animal stomachs, in which milk can be turned into cheese. With the development of humanity history, enzymes have been gradually applied into various fields like clinical therapy and chemical production. In particular, enzymes have been used in the diagnosis of disease since the 1940's, derived from the intensive research in biochemistry. What are enzymes? How they work in biological reactions and living organisms? What factors bring influences on the enzymatic reactions? What are the applications of enzymes in biotechnology and medical research? Here, you can find what we have summarized.