Methionine is one of the most hydrophobic, redox-sensitive, and one of the only two sulfur-containing amino acids on protein. Because of these biochemical properties, the methionine residue plays a central role in a variety of biological processes, such as metal coordination, antioxidant stress, and aging. However, studies on the molecular functions of methionine are much less common than the other primary sulfur-containing amino acid, cysteine. The limited number of publications on methionine-related studies is partially due to the lack of tools for methionine modification. Methionine bioconjugation offers a new strategy to decipher the biological function of methionine and expands the toolbox for protein functionalization in the context of the application, such as synthesizing proteins with novel properties and producing new biomaterials. The purpose of this Perspective is to highlight the biochemical properties and functions of methionine, list recent progress in the development of methionine bioconjugation reagents, and briefly demonstrate the application of these reagents on polypeptides, proteins, and proteomes.