Azido-PEG4-nitrile is a versatile specialty chemical widely used in bioconjugation and click chemistry applications. It features an azide functional group for efficient and selective reactions with alkyne-containing compounds via copper-free or catalyzed click reactions, a PEG4 spacer to enhance water solubility, reduce steric hindrance, and improve biocompatibility, and a terminal nitrile group that serves as a reactive handle for further functionalization, such as conversion to tetrazoles or amidation. This compound is particularly valuable in the development of bioconjugates, including antibody-drug conjugates (ADCs), where it acts as a linker to connect therapeutic agents to targeting molecules, enhancing the stability and efficacy of the resulting assemblies. In materials science, it enables surface modification and functionalization of nanoparticles, polymers, and biomaterials for creating advanced materials with tailored properties. Its applications also extend to drug delivery systems, facilitating the controlled release of active pharmaceutical ingredients, and in vaccine development for targeted conjugation.