Yasutaka Ihara (伊原 康隆, Ihara Yasutaka; born 1938, Tokyo Prefecture) is a Japanese mathematician and professor emeritus at the Research Institute for Mathematical Sciences.
Ihara received his PhD at the University of Tokyo in 1967 with thesis Hecke polynomials as congruence zeta functions in elliptic modular case.
In 1990, Ihara gave a plenary lecture Braids, Galois groups and some arithmetic functions at the ICM in Kyōto.
[1] Ihara has worked on geometric and number theoretic applications of Galois theory.
[2] In graph theory the Ihara zeta function has an interpretation, which was conjectured by Jean-Pierre Serre and proved by Toshikazu Sunada in 1985.