Tadeusz Kotarbinski (Polish: ['kotarbinski]; 31 March 1886 – 3 October 1981) was a Polish philosopher, logician and ethicist.
A pupil of Kazimierz Twardowski, he was one of the most representative figures of the Lwów–Warsaw School, and a member of the Polish Academy of Learning (PAU) as well as the Polish Academy of Sciences (PAN).
He developed philosophical theory called reism (Polish: reizm) and an ethical system called independent ethics.
Kotarbinski also contributed significantly to the development of praxeology.
Henryk Greniewski and Kazimierz Pasenkiewicz were doctoral students under Kotarbinski.