Theodor Georg Andreas Molien (Russian: Fedor Eduardovich Molin; 10 September [O.S. 29 August] 1861 in Riga – 25 December 1941 in Tomsk) was a Russian mathematician of Baltic German origin. He was born in Riga, Latvia, which at that time was a part of Russian Empire. Molien studied associative algebras and polynomial invariants of finite groups.