Dehydrogenation plays a very important role in both nature and human civilization. In chemical industry, dehydrogenations are used to produce propene, butene, butadiene, isobutene, and isopropene from the corresponding alkanes. In living organisms (both animals and plants), respiration is actually a process of oxidation wherein some steps involve dehydrogenation. Almost all dehydrogenation reactions require a catalyst. Catalysts for dehydrogenation can be classified into two main categories: conventional catalysts (including inorganic and organic) and enzymes. This article focuses on the application of biological catalysts in dehydrogenation and oxidation reactions occurring in nature. Biological dehydrogenation is illustrated from two aspects: chemistry of biocatalytic dehydrogenation and biocatalysts of dehydrogenation. Biological dehydrogenation reactions usually occur at very mild conditions and have very high selectivity. The catalysts for these processes are usually enzymes (or cells producing these enzymes). Enzymes having dehydrogenation capacities are usually dehydrogenases, oxidases, etc., and most of them need a coenzyme or a cofactor to work with them.