Industry has an increasing interest in the use of enzymes as environmentally friendly, highly efficient, and specific bio-catalysts. Enzymes have primarily evolved to function in aqueous environments at ambient temperature and pressure. These conditions however do not always correspond with industrial processes or applications, and only a small portion of all known enzymes are therefore suitable for industrial use. Protein engineering can sometimes be applied to convey more desirable properties to enzymes, such as increased stability, but is limited to the 20 naturally occurring amino acids or homologs thereof. Using post-production modification, which has the potential to combine desirable properties from the enzyme and the conjugated compounds, enzymes can be modified with both natural and synthetic molecules. This offers access to a myriad of possibilities for tuning the properties of enzymes. At this moment, however, the effects of post-production modification cannot yet be reliably predicted. The increasing number of applications will improve this so that the potential of this technology can be fully exploited. This review will focus on post-production modification of enzymes and its use and opportunities in industry.