Ilya Mikhailovich Frank (Russian: Илья Михайлович Франк; 23 October 1908 – 22 June 1990) was a Soviet physicist who received the 1958 Nobel Prize in Physics, jointly with Pavel Alekseyevich Cherenkov and Igor Y. Tamm, also of the Soviet Union.

His father, Mikhail Lyudvigovich Frank, was a talented mathematician descended from a Jewish family, while his mother, Yelizaveta Mikhailovna Gratsianova, was a Russian Orthodox physician.

Ilya's uncle, Semyon Frank, a noted Russian philosopher, wasn't as fortunate and was expelled from the USSR in 1922 together with 160 other intellectuals.

Ilya had one elder brother, Gleb Mikhailovich Frank, who became an eminent biophysicist and member of the Academy of Sciences of the USSR.

He became interested in the effect discovered by Pavel Cherenkov, that charged particles moving through water at high speeds emit light.

Together with Igor Tamm, he developed a theoretical explanation: the effect occurs when charged particles travel through an optically transparent medium at speeds greater than the speed of light in that medium, causing a shock wave in the electromagnetic field.