 Nyāya is a multi-dimensional system of interlocking views that belies the stereotype of Indian philosophy as idealist and mystical in orientation. The school’s founding text is the Nyāya-sūtra (c. 100 CE), which had elicited tomes of commentary long before Gaṅgeśa. Nyāya is broadly realist about objects talked about and experienced everyday. Gaṅgeśa advances what may be called a reliabilist theory of knowledge and justification, indeed a super-reliabilism, an infallibilism for externalists in the sense that sources of knowledge—perception, inference, analogy, and testimony, his main focus—are conceived factively. Among his most major accomplishments are definitions of knowledge in general and of natural “pervasions” as underpinning inference as well as analyses of conditions governing meaning in knowledge-transfers through testimony. He is also known for crisp treatments of the major types of fallacy and epistemic defeater. Gaṅgeśa presents, defending in long passages, (a) an argument for a self as a special type of substance, (b) a theistic argument that illustrates his theory of debate and reasoning in great detail, and (c) a defense of the possibility of “liberation,” mukti, that both enlivens the views of very early Nyāya—in particular Vātsyāyana (c. 400 CE)—and becomes influential in several other traditions and schools. Nyāya itself has a lively literature that extends to the modern period and, among the traditionally learned, to our own day.