Sergiu Klainerman (born May 13, 1950) is a mathematician known for his contributions to the study of hyperbolic differential equations and general relativity.

After attending the Petru Groza High School,[2] he studied mathematics at the University of Bucharest from 1969 to 1974.

[3] His thesis, written under the direction of Fritz John and Louis Nirenberg, was titled Global Existence for Nonlinear Wave Equations.

[4] From 1978 to 1980 Klainerman was a Miller Research Fellow at the University of California, Berkeley, while from 1980 to 1987 he was a faculty member at New York University's Courant Institute of Mathematical Sciences, rising in rank to Professor in 1986.

[10] Klainerman was awarded the Bôcher Memorial Prize by the American Mathematical Society in 1999 "for his contributions to nonlinear hyperbolic equations".