Alcohol dehydrogenases (ADHs; EC 1.1.1.1), a subset of oxidoreductases requiring NAD(P) as a cofactor, are present virtually in all life forms. Among them, Group I ADHs are Zn-dependent enzymes of ca. 350 amino acid residues. Owing to biochemical characterization and crystallographic studies on Group I ADHs allowing for information on structure-function relationship, much knowledge is available on the role of specific amino acid residues. Over the last decade a significant amount of work has been done also on molecular characterization of bacterial and yeast Group I ADHs, making it possible to estimate, among others, structure-function relationships in the ADHs for which only primary structure is available. In this paper we review the role of conserved amino acid residues of well characterized microbial NAD(P) and Zn-dependent ADHs in catalysis, sequestration of catalytic and structural zinc, cofactor binding and substrate specificity.