The cGAS-STING pathway is a central mechanism of innate immunity that detects double-stranded DNA and translates it into transcriptional and other cellular effector responses. Beyond its canonical role in antiviral defense, the pathway senses diverse endogenous DNA species generated as byproducts during various contexts of cell stress. In this capacity, cGAS-STING impacts tissue homeostasis and antitumor immunity, but it is also associated with a number of inflammatory disorders. Here, we review the mechanisms, physiological functions, and disease implications of cGAS-STING signaling and discuss how its context-dependent biology informs emerging therapeutic strategies.