Ilya Mikhailovich Lifshitz (Ukrainian: Ілля́ Миха́йлович Лі́фшиць, Russian: Илья́ Миха́йлович Ли́фшиц; January 13, 1917 – October 23, 1982) was a leading Soviet theoretical physicist, brother of Evgeny Lifshitz.

[1][2] Ilya Lifshitz was born into a Ukrainian Jewish family in Kharkov, Kharkov Governorate, Russian Empire (now Kharkiv, Ukraine).

Together with Arnold Kosevich, in 1954 Lifshitz established the connection between the oscillation of magnetic characteristics of metals and the form of an electronic surface of Fermi (Lifshitz–Kosevich formula) from de Haas–van Alphen experiments.

In perturbation theory, Lifshitz introduced[4] the notion of spectral shift function, which was later developed by Mark Krein.

Grosberg and Alexei R. Khokhlov, Lifshitz proposed a theory of coil-to-globule transition in homopolymers and derived the formula for the conformational entropy of a polymer chain, that is referred to as the Lifshitz entropy.