Bardaisan (11 July 154 - 222 AD; , Bar Daysan; also Bardaisan), known in Arabic as ibn Daysan and in Latin as Bardesanes, was a Syriac-speaking Christian writer and teacher with a Gnostic background, and founder of the Bardaisanites.

A scientist, scholar, astrologer, philosopher, hymnwriter, and poet, Bardaisan was also renowned for his knowledge of India, on which he wrote a book, now lost. According to the early Christian historian