Innate immunity is a key pathway activated in response to bacterial and viral infections. The invasion of foreign nucleic acids results in the production of interferons and cytokines that comprise the host defense. More recently, roles for innate immunity in tumorigenesis, autoimmune disease, and senescence also have been elucidated. In these diseases, it is ‘self’ nucleic acids, RNA and DNA, which escape into the cytosol and trigger immune responses. Cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) are the key sensors of nucleic acids in the immunity pathway.