Catalytic transformations have shown the great utility in chemical modification of proteins from various viewpoints, and the collection and analysis of a set of literature in this review also underscored possible future directions of the realm of the catalytic bioconjugation research. Appearance of redox-mediated chemistry in a multitude of sections is notable, probably implying its growing interests across various catalysis fields. However, because oxidation and reduction reactions are common processes in several canonical amino acid side chains, 279 strategies to suppress unwanted side reactions may be the unavoidable tasks as literature precedents also tackled the issue already (e.g., reactions under inert atmosphere 280 and use of redox-sensitive additives 281 ). It became also obvious that some catalytic strategies are limited to only a certain reaction type or virtually non-existent for protein bioconjugation purposes. For instance, organocatalysis and heterogeneous catalysis have been realized only through acyl-transfer reactions and backbone hydrolysis, respectively. We were unable to find any examples of asymmetric catalysis and mechanochemical catalysis that have been used for bioconjugation at a protein level, though potential usefulness of some reactions for small molecule substrates in this areas are indicated in recent literature. In particular, the dearth of the asymmetric catalysis is striking given the enantiomeric/geometric importance of post-translational modification in nature (e.g., methionine oxidation 284 and lysine acetylation 285 ) as well as increasing studies on d-amino acid/dproteins. Dehydroalanine functionalization would be an example highlighting this trend, as there have not been examples of protein bioconjugation utilizing dehydroalanine in an asymmetric fashion even if a plethora of reports demonstrated asymmetric conjugate addition reactions at a small molecule level. Plausibly, this challenge may have been exacerbated by limited availability of analytical techniques that can be usable to differentiate the isomer forms of a particular amino acid residue in protein substrates. The examination of literature also showed the power of dual catalytic systems, especially those combined with supramolecular catalysis for sitespecific or target-specific labeling strategies. Indeed, hybrid catalytic systems have been frequently utilized in chemistry of small molecules and peptides, 289 and protein bioconjugation may benefit from such hybrid systems as well. Finally, it is noteworthy that some catalytic mechanisms would be only possible in polypeptide substrates but not simple small molecule substrates (e.g., copper-catalyzed backbone modification of amide N-H driven by a neighboring histidine residue 132 ), and proteins may serve as a platform to expand the boundary of the catalysis domain beyond the small molecule chemistry. Diverse fields spanning bioorganic chemistry, chemical biology, biomedical science, and material science necessitate development of protein bioconjugation to address various scientific and pragmatic challenges, and the chemical strategies and principles mentioned in this review paper may be a catalyst to transcend the limit.