Paul Walden (Latvian: Pauls Valdens; Russian: ????? ???????? ???????; German: Paul von Walden; 26 July 1863 – 22 January 1957) was a Russian, Latvian and German chemist known for his work in stereochemistry and history of chemistry.
In particular he invented the stereochemical reaction known as Walden inversion and synthesized the first room-temperature ionic liquid, ethylammonium nitrate.