Poly(L-Arginine) is a cationic poly(amino acid) with guanidinium side chains, positively charged in aqueous solution. It exhibits excellent water solubility, strong cell-penetrating ability, and high binding affinity to negatively charged nucleic acids, proteins, and cell membranes. Biocompatible and biodegradable, it is widely used in gene delivery, cell adhesion coating, biomaterial functionalization, and antibacterial applications.