Lazar Aronovich Lyusternik (also Lusternik, Lusternick, Ljusternik; Russian: Лазарь Аронович Люстерник; 31 December 1899 – 22 July 1981) was a Soviet mathematician.

He is famous for his work in topology and differential geometry, to which he applied the variational principle.

The ellipsoid with distinct but nearly equal axis is the critical case with exactly three closed geodesics.

The Lusternik–Schnirelmann theory, as it is called now, is based on the previous work by Poincaré, David Birkhoff, and Marston Morse.

In addition to serving as a professor of mathematics at Moscow State University, Lyusternik also worked at the Steklov Mathematical Institute (RAS) from 1934 to 1948 and the Lebedev Institute of Precise Mechanics and Computer Engineering (IPMCE) from 1948 to 1955.