PEGylation is a pharmaceutical technology that involves the covalent attachment of polyethylene glycol (PEG) to a drug to improve its pharmacokinetic, pharmacodynamic, and immunological profiles, and thus, enhance its therapeutic effect. Currently, PEGylation is used to modify proteins, peptides, oligonucleotides, antibody fragments, and small organic molecules. Research groups are striving to improve the consistencies of PEGylated drugs and to PEGylate commercialized proteins and small organic molecules. Furthermore, the PEGylations of novel medications, like oligonucleotides and antibody fragments, are being pursued to improve their bioavailabilities. This active research in the PEGylation field and the continued growth of the biopharmaceutical market predicts that PEGylated drugs have a bright future.