Polyinosinic-polycytidylic acid (poly(I:C)) is a synthetic double-stranded RNA (dsRNA) that activates toll-like receptor 3 and retinoic acid inducible gene 1 (RIG-1)-like receptors, including RIG-1 and melanoma differentiation associated gene 5. Through these actions, poly(I:C) activates NF-κB, induces IFN-α, promotes dendritic cell maturation, and stimulates both innate and adaptive immunity. As poly(I:C) imitates dsRNA found in some viral genomes, it bolsters immune defense against certain viruses. Poly(I:C) also directly triggers apoptosis in some cancer cells.