Biotransformations involve mainly microorganisms or individual enzymes applied to catalyze chemical reactions . This field of science is particularly important, because it allows to obtain optically active compounds, which are valuable raw materials for pharmaceutical (Fig. 3, Fig. 6, Fig. 20, Fig. 21), wood and paper (Fig. 18), food (Fig. 4), textile (Fig. 12), cosmetic (Fig. 14) industries and environmental protection (Fig. 19). Oxidoreductases, in particular alcohol dehydrogenases (E.C.188.8.131.52, ADH) are valuable biocatalysts enabling to obtain enantiomerically pure products. These enzymes, commonly found in nature, catalyze both oxidation and reduction reactions . Described dehydrogenases descend from mesophilic, psychrophilic and thermophilic microorganisms. The increasing application of thermophiles is due to their exceptional resistance against heat and organic solvents. The article describes and explains how microbial ADH’s interact with NAD+/NADH or NADP+/NADPH and present those enzymes which catalyze reactions with both forms of cofactors. The alcohol dehydrogenases from yeast are particularly commonly used [9–14]. Bacterial enzymes, among them ADH isolated from Thermoanaerobacter brockii [47–51], are widely distributed too. In addition, the literature describes a number of (R)-specific ADH’s from Lactobacillus kefir [40–42], L. brevis [45, 46], Leisofonia sp.  Pseudomonas fluorescens  and (S)- -specific ADH’s from Rhodococcus erythropolis [15, 16], Thermus sp. , Sulfolobus solfataricus [23, 28] and many others.