Ratnakīrti (11th century CE) was an Indian Buddhist philosopher of the Yogācāra and epistemological (pramāṇavāda) schools who wrote on logic, philosophy of mind and epistemology. Ratnakīrti studied at the Vikramaśīla monastery in modern-day Bihar. He was a pupil of Jñānaśrīmitra, and Ratnakīrti refers to Jñānaśrīmitra in his work as his guru with phrases such as yad āhur guravaḥ.

Ratnakīrti's work has been termed as "more concise and logical though not so poetical" compared to that of his teacher, although he does build on much of Jñānaśrīmitra's work.

Ratnakīrti was active sometime between 1000 and 1050 CE. Among his contemporaries at Vikramashila were Ratnākaraśānti and Jñanasrimitra. Ratnakīrti engaged with both of them on an intellectual level and it is clear that Ratnakīrti was Jñānaśrīmitra's student on subjects relating to logico-epistemological topics as the former often quotes the latter as his "guru".

With Ratnākaraśānti, the relationship was more complex as it is likely that Ratnakīrti was his pupil on topics related to tantra however Yuichi Kajiyama states that "Ratnākaraśānti learned Buddhism, exoteric and esoteric, under Ratnakīrti and others."

Ratnakīrti's Refutation of Other Mindstreams (Santānāntaradūṣaṇa) argued that knowledge of external streams of consciousness (citta-santāna) is a form of inference (anumāna) and not direct perception (pratyakṣa). Ratnakīrti introduced the two truths doctrine as key to the nature of the discussion. Since inference deals with conceptual universals, the proof of the mindstreams of others, while empirically valid in relative truth (saṃvṛtisatya), does not hold ultimate metaphysical certainty in absolute truth (paramārthasatya). Ratnakīrti, therefore argued that at the ultimate level, there is only an undifferentiated non-dual consciousness (vijñānādvaita) since one cannot differentiate consciousness as a whole into different individual minds.

Ratnakīrti quotes from Jñānaśrīmitra's Sākārasiddhiśāstra:

If one’s own mind is distinct from another by nature, it should appear together with a limiting object (avadhi), [i.e., another mind]. [Therefore, one’s own mind should not be distinct from another.] Nor should it be apprehended that [one’s own mind] is identical with [another mind].

This means that any knowledge of a distinction between two things depends on perceiving those two things, and seeing how they are different. However, one can only perceive one's own mind. Therefore, one’s mind cannot be shown to be distinct from other minds (at the same time, one's own mind also cannot be shown to be identical to other minds since, again, this knowledge would be based on perceiving other minds as well). Roy Perrett explains, "Our knowledge of distinction depends upon our knowledge of two things, but we only perceive our own minds. There is, then, no way to draw a boundary (avadhi) between distinct psychological streams, and no way to individuate minds."