4-Azido-L-phenylalanine hydrochloride is widely used in bioorthogonal chemistry and protein engineering. It serves as a non-natural amino acid that can be incorporated into proteins through genetic code expansion techniques. Once incorporated, the azido group enables selective labeling or modification of the protein using click chemistry, particularly via the azide-alkyne cycloaddition reaction. This makes it a valuable tool for studying protein function, localization, and interactions in living cells. Additionally, it is utilized in the development of bioconjugates for targeted drug delivery and imaging applications, as well as in the synthesis of biomaterials with tailored properties. Its ability to introduce specific functionalities into proteins without disrupting their native structure has made it a key reagent in chemical biology and biomedical research.