Isidor Pavlovich Natanson (Russian: Исидор Павлович Натансон; February 8, 1906 in Zurich – July 3, 1964 in Leningrad) was a Swiss-born Soviet mathematician known for contributions to real analysis and constructive function theory, in particular, for his textbooks on these subjects.[1] His son, Garal'd Natanson (1930–2003), was also a known mathematician.[2]