PEGylation is the process of both covalent and non-covalent attachment or amalgamation of polyethylene glycol (PEG, in pharmacy called macrogol) polymer chains to molecules and macrostructures, such as a drug, therapeutic protein or vesicle, which is then described as PEGylated. PEGylation is routinely achieved by the incubation of a reactive derivative of PEG with the target molecule. The covalent attachment of PEG to a drug or therapeutic protein can “mask” the agent from the host’s immune system (reducing immunogenicity and antigenicity), and increase its hydrodynamic size (size in solution), which prolongs its circulatory time by reducing renal clearance. PEGylation can also provide water solubility to hydrophobic drugs and proteins. Having proven its pharmacological advantages and acceptability, PEGylation technology is the foundation of a growing industry.