The Nyayavatara is one of the first serious Jaina treatises on epistemology. It has been for long erroneously ascribed by tradition to Siddhasens Divakara, but now it seems certain that its author is a certain Siddhasens Mahamati, who lived circa 710/720-700/780. He enters into polemics with other-mostly Buddhist- epistemological schools and endeavours to establish a Jaina epistemological tradition of its own. Despite its importance, the work is rather secondary in the sense that it relies, for the most part, on the Buddhist logical legacy. The first extant commentary is the Nyayavatara vivrti of Siddharsiganin. Although its significance has often been under-estimated, Siddhsiganin was responsible for the subsequent development of Jaina epistemological thought to a much larger degree than it has so far been recognized. He refers to major philosophical schools of his times, e.g. to Sautrantika, Yogacara, Sunyavada, Saugata, Samkhya, Mimamsa, Naiyayika Vaisesika, Carvaka, Advaita-vedanta, the materialists, etc. The gloss (Nyayavatara-tippana) of Dvebhadrasure, which is amply quoted in the present edition, is a useful source of quotations.