Ilya Frank was born on 23 October 1908 in St. Petersburg. 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. His father participated in the student revolutionary movement, and as a result was expelled from Moscow University. After the October Revolution, he was reinstated and appointed professor. 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.