The Rhizopus spp., in particular Rhizopus oryzae, are among the most frequently used whole cell biocatalysts. The fungus is known to catalyze the bioconversion of various reactive and non-reactive substrates with high regio- and stereoselectivities. The range of products obtained from these reactions has been attributed to the substrate binding modes within the enzymes active site. More recently, an active site model has been developed to account for the reported bioconversions. The use of this model will prove useful in future synthetic and biotechnological applications.