Azido-PEG-Hydrazide is a compound that belongs to the family of polyethylene glycol (PEG) derivatives. It contains two important functional groups, the azide and the hydrazide groups, which make it a valuable tool in pharmaceutical research and development. The azide group enables the compound to react with other molecules containing terminal alkynes through copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, also known as “click chemistry”. This reaction allows for the efficient attachment of Azido-PEG-Hydrazide to various molecules of interest, including drugs, peptides, and proteins. On the other hand, the hydrazide group can react with carbonyl-containing molecules, such as aldehydes and ketones, forming hydrazone linkages, which are often used in drug delivery systems.