Prince Nikolai Sergeyevich Trubetzkoy[1] (Russian: Николай Сергеевич Трубецкой, IPA: [trʊbʲɪtsˈkoj]; 16 April 1890 – 25 June 1938) was a Russian linguist and historian whose teachings formed a nucleus of the Prague School of structural linguistics.

While spending some time at the University of Leipzig, Trubetzkoy was taught by August Leskien, a pioneer of research into sound laws.

[3] He died from a heart attack attributed to Nazi persecution after he had published an article that was highly critical of Hitler's theories.

His magnum opus, Grundzüge der Phonologie (Principles of Phonology)[4] was issued posthumously in which he defined the phoneme as the smallest distinctive unit within the structure of a given language.

According to Aczel, Trubetzkoy's focus in Principles of Phonology was the study of phonemes and their opposing aspects to describe rules of language, the goal of describing general underlying rules being the common goal of structuralism.