Ira Borah Bernstein (born November 8, 1924) is an American theoretical physicist specializing in plasma physics. He was the first person to formulate the theory of electrostatic waves propagating in a magnetized plasma in 1958, which are now commonly known as Bernstein waves in plasma physics. Bernstein's other theoretical contributions include the development of the energy principle in the study of plasma instabilities, as well as formulating the exact (one-dimensional) solution to electrostatic wave propagation in an unmagnetized plasma also known as Bernstein–Greene–Kruskal modes.