Vadim Arsen'evič Efremovič (Вади́м Арсе́ньевич Ефре́мович: c. 1903 - May 1, 1989) was a Soviet mathematician. (The spelling "Efremovic" is often seen.)
Efremovič was a member of the Moscow Topological School, and specialized in the geometric aspects of general topology. He introduced the notion of proximity spaces at the First International Topological Conference in Moscow in 1934. He was imprisoned from 1937 to 1944, and did not publish on proximity spaces until 1951, at which point the theory was developed rapidly by Efremovič and associates.
Efremovič also introduced the notion of "volume invariants" for "equimorphisms" (that is, uniformly bicontinuous) on metric spaces. These have proven to be very important in the study of manifolds and hyperbolic geometry.