The use of natural catalysts -enzymes -for the transformation of non-natural man-made organic compounds is not at all new: they have been used for more than one hundred years, employed either as whole cells, cell organelles or isolated enzymes [1, 2]. Certainly, the object of most of the early research was totally different from that of the present day. Thus the elucidation of biochemical pathways and enzyme mechanisms was the main reason for research some decades ago. It was mainly during the 1980s that the enormous potential of applying natural catalysts to transform non-natural organic compounds was recognized. What started as a trend in the late 1970s could almost be called a fashion in synthetic organic chemistry in the 1990s. Although the early euphoria during the 'gold rush' in this field seems to have eased somewhat, there is still no limit to be seen for the future development of such methods. As a result of this extensive, recent research, there have been an estimated 12000 papers published on the subject. To collate these data as a kind of 'super-review' would clearly be an impossible task and, furthermore, such a hypothetical book would be unpalatable for the non-expert [3-6].

1 Introduction and Background Information.- 1.1 Introduction.- 1.2 Common Prejudices Against Enzymes.- 1.3 Advantages and Disadvantages of Biocatalysts.- 1.3.1 Advantqages of Biocatalysts.- 1.3.2 Disadvantages of Biocatalysts.- 1.3.3 Isolated Enzymes versus Whole Cell Systems.- 1.4 Enzyme Properties and Nomenclature.- 1.4.1 Mechanistic Aspects.- 1.4.2 Classification and Nomenclature.- 1.4.3 Coenzymes.- 1.4.4 Enzyme Sources.- References.- 2 Biocatalytic Applications.- 2.1 Hydrolytic Reactions.- 2.1.1 Mechanistic and Kinetic Aspects.- 2.1.2 Hydrolysis of the Amide Bond.- 2.1.3 Ester Hydrolysis.- 2.1.3.1 Esterases and Proteases.- 2.1.3.2 Lipases.- 2.1.4 Hydrolysis and Formation of Phosphate Esters.- 2.1.5 Hydrolysis of Epoxides.- 2.1.6 Hydrolysis of Nitriles.- References.- 2.2 Reduction Reactions.- 2.2.1 Recycling of Cofactors.- 2.2.2 Reduction of Aldehydes and Ketones Using Isolated Enzymes.- 2.2.3 Reduction of Aldehydes and Ketones Using Whole Cells.- 2.2.4 Reduction of C=C-Bonds Using Whole Cells.- References.- 2.3 Oxidation Reactions.- 2.3.1 Oxidation of Alcohols and Aldehydes.- 2.3.2 Oxygenation Reactions.- 2.3.2.1 Hydroxylation of Alkanes.- 2.3.2.2 Hydroxylation of Aromatic Compounds.- 2.3.2.3 Epoxidation of Alkenes.- 2.3.2.4 Sulfoxidation Reactions.- 2.3.2.5 Baeyer-Villiger Reactions.- 2.3.2.6 Formation of Peroxides.- 2.3.2.7 Dihydroxylation of Aromatic Compounds.- References.- 2.4 Formation of Carbon-Carbon Bonds.- 2.4.1 Aldol-Reactions.- 2.4.2 Acyloin-Reactions.- 2.4.3 Michael-Type Additions.- References.- 2.5 Addition and Elimination Reactions.- 2.5.1 Cyanohydrin Formation.- 2.5.2 Addition of Water and Ammonia.- References.- 2.6 Glycosyl-Transfer Reactions.- 2.6.1 Glycosyl Transferases.- 2.6.2 Glycosidases.- References.- 2.7 Halogenation and Dehalogenation Reactions.- 2.7.1 Halogenation.- 2.7.2 Dehalogenation.- References.- 3 Special Techniques.- 3.1 Enzymes in Organic Solvents.- 3.1.1 Ester Synthesis.- 3.1.2 Lactone Synthesis.- 3.1.3 Amide Synthesis.- 3.1.4 Peptide Synthesis.- 3.1.5 Peracid Synthesis.- 3.1.6 Redox Reactions.- 3.1.7 Medium Engineering.- 3.2 Immobilization.- 3.3 Modified and Artificial Enzymes.- 3.3.1 Modified Enzymes.- 3.3.2 Semisynthetic Enzymes.- 3.3.3 Catalytic Antibodies.- References.- 4 State of the Art and Outlook.- 5 Appendix.- 5.1 Abbreviations.- 5.2 Suppliers of Enzymes.- 5.3 Commonly Used Lipase Preparations.- 5.4 Major Culture Collections.- 5.5 Pathogenic Bacteria and Fungi.