Mikołaj Habdank Kruszewski, (Russianized, Nikolay Vyacheslavovich Krushevsky, Никола́й Вячесла́вович Круше́вский) (December 18, 1851, Lutsk – November 12, 1887, Kazan) was a Polish linguist, most significant as the co-inventor of the concept of phonemes, and relative of Anya Lucia Kruszewski. From 1883, he was a professor at Kazan University. His notable works include On Sound Alternation (1881) and Outline of Linguistic Science (1883). The former is actually the introduction to his master's thesis on morphophonemic alternation in Old Slavic (the section focusing on the theoretical background for the empirical work in the body of the thesis) and the latter is his doctoral thesis.
A student of Jan Baudouin de Courtenay (1845–1929), Kruszewski worked with de Courtenay to develop the linguistics associated with the Kazan school. These inspired other linguists. Since it is difficult to distinguish who created which concept, the systematic treatment of alternation may be attributed to both. Their innovative and highly influential work has been acclaimed by Roman Jakobson only about a hundred years after his time.