Andrey Nikolayevich Tikhonov (; October 30, 1906 – October 7, 1993) was a Soviet and Russian mathematician and geophysicist known for important contributions to topology, functional analysis, mathematical physics, and ill-posed problems. He was also one of the inventors of the magnetotellurics method in geophysics. Tikhonov's surname is also transliterated as "Tychonoff", because he originally published in German. Other forms of his name include "Tychonov", "Tihonov", "Tichonov."