Isolated enzymes or whole microbial cells are environmentally friendly catalysts which can be used in aqueous solution at room temperature, atmospheric pressure, and moderate pH values and are therefore well suited for the green synthesis of novel drugs. Microbial enzymes transform numerous substances in a reaction-, region-, and stereospecific way and thus in many cases may meet the requirements of modern drug synthesis. Of particular practical value is the fact that they not only catalyze the reactions of their natural substrates but also convert other compounds. Biotechnological processes use whole cells and/or specific enzymes. Biosynthetic processes, which often require a cascade of individual enzyme reactions, are usually carried out with whole cells, whereas biotransformation reactions use either isolated enzymes or whole cells depending on the properties of the enzymes involved. When evaluating a process, the advantages and disadvantages of isolated enzymes and whole cells must be weighed against each other, though where possible, specific enzymes tend to be preferred so as to exclude side reactions catalyzed by cells. This Special Issue will provide an insight into strategies of biosynthesis and biotransformation of novel drugs. The latest proven enzyme-mediated routes, using single-step biotransformation or enzyme cascade synthesis, will be discussed.