Udayana, also known as Udayanācārya (Udyanacharya, or Master Udayana), was a very important Hindu logician of the tenth century who attempted to reconcile the views held by the two major schools of logic (Nyaya and Vaisheshika).[2][3][4] This became the root of the Navya-Nyāya ("New Nyāya") school of the thirteenth century, established by the Gangesha Upadhyaya school of "right" reasoning, which is still recognized and followed in some regions of India today. He lived in Kariyan village in Mithila, near present-day Darbhanga, Bihar state, India.

Udayana wrote a sub-gloss on Vachaspati's work called the Nyaya-vaartika-taatparya-tiikaa-parishuddhi.[5] He wrote several other works such as the Kusumanjali, Atma-tattva-viveka, Kiranaavali and Nyaya-parishishhta (also called Bodha siddhi or Bodha shuddhi).

He is given credit by Naiyâyikas for having demolished in a final fashion the claims of the Buddhist logicians.[6][7] All his known works are thought to have been preserved, attesting to the importance given to him in Indian philosophy.[8]

Udayana's Nyayakusumanjali gave the following nine arguments to prove the existence of a creative God.[9][10][11]

Seven works have been ascribed to Udayana. The following are the titles of the works in the chronological order in which they are believed to have been composed.[12]