The Masurian ethnolect (Masurian: mazurská gádkä; Polish: mazurski; German: Masurisch), according to some linguists, is a dialect group of the Polish language; others consider Masurian to be a separate language, spoken by the Masurian people in northeastern Poland.

From the 14th century, some settlers from Masovia started to settle in southern Prussia, which had been devastated by the crusades of the Teutonic Knights against the native Old Prussians. According to other sources, people from Masovia did not move to southern Prussia until the time of the Protestant Reformation, Prussia having become Lutheran in 1525. The Masurians were mostly of the Protestant faith, in contrast to the neighboring Roman Catholic people of the Duchy of Masovia, which was incorporated into the Polish kingdom in 1526. A new dialect developed in Prussia, isolated from the remaining Polish language area. The Masurian dialect group has many Low Saxon, German and Old Prussian words mixed in with Polish-language endings.^[3]

Beginning in the 1870s, Imperial German officials restricted the usage of languages other than German in Prussia's eastern provinces.^[4] While in 1880 Masurians were still treated as Poles by the German Empire, at the turn of century the German authorities undertook several measures to Germanise and separate them from the Polish nation by creating a separate identity.^[5] After World War I the East Prussian plebiscite was held on July 11, 1920, according to the Treaty of Versailles, in which the Masurians had to decide whether they wanted to be part of the Second Polish Republic or remain in German East Prussia; about 98% voted for Germany.

By the early 20th century, most Masurians were at least bilingual and could speak Low Saxon and German; in some areas about half of them still spoke Masurian, at least at home. In 1900, according to the German census there were 142,049 Masurians speaking Masurian.^[6] In 1925, only 40,869 people gave Masurian as their native language, many considering German their first language, considering Masurian merely as their domestic dialect, By the early 1920s there were also some Masurians who had their separate identity, claiming that Masurians are a nation. Most of them were members of Masurenbund. Their main goal was to grant Masurians some minority laws inside Germany, but there were also some separatists. In the early 1930s, support for the Nazi Party was high in Masuria, especially in elections in 1932 and 1933. Nazi political rallies were organized in the Masurian dialect during the campaigning.^[4]

After 1933 the usage of the Masurian dialect was prohibited by the National Socialist authorities. By 1938 most Masurian place and personal names had been changed to "pure" German substitutes. From 1939 on it was forbidden to hold church services in Masurian.

The replacement of Masurian in favor of German was not completed by the time the Soviet Red Army conquered Masurian East Prussia in January 1945, in World War II. The territory was transferred to Poland according to the postwar Potsdam Conference. During the wartime fighting and post-war deportations in the subsequent decades, most Masurian-speakers left Masuria for western Germany, especially to post-war West Germany, where they were quickly assimilated into the German mainstream.

The oldest book written in Masurian probably is Ta Swenta Woyna, written by Jakub Szczepan in 1900.^[18]

In 2018, The Little Prince by Antoine de Saint Exupéry was translated to Masurian.^[19]

Several scientists consider Masurian to be a separate language in its own right;^[20][21][22] others argue that Masurian is a dialect of Polish, or even just a subdialect.^[23]

• Mazuration (Polish: mazurzenie): the dentalization of the Standard Polish retroflex consonants /tʂ, dʐ, ʂ, ʐ/ to /ts, dz, s, z/
• Possible fricativization of /j/ in /pj, bj, fj, vj/ (when they correspond to the historical palatalized labials /pʲ, bʲ, fʲ, vʲ/) to /pɕ, bʑ, fɕ, vʑ/ or sometimes depalatalization
• A change of /mj/ to /ɲ/
• The post-palatals [kʲ, ɡʲ, xʲ] are sometimes fronted to the alveolo-palatal [tɕ, dʑ, ɕ], similarly to Kashubian
• Labialization of the vowel o (sometimes also u) initially
• The standard vowel [ɘ] (typically transcribed with ⟨ɨ⟩ in IPA) is fronted to [ɪ], as in Czech
• /i/, /ɨ/ and /u/ all merge into /u/ before /w/, e.g. buł /buw/, zuł /zuw/ (był, żył)
• Denasalization of the nasal vowels ą and ę to o and e
• In some varieties ę becomes ã (nasal a), which is pronounced after denasalization an. Analogous changes occur for groups eN, like dzień – dzian
• Hardening of the consonants /ɕ ʑ/ to /ʃ ʒ/

Masurian has three to five dialects:^[24]

• Ostróda dialect (Ostróda, Olsztynek) – Denasalization of the nasal vowels ą and ę as o and e – No mazuration – Common á (ɒ, a result from historic long vowels. See Old Polish phonology and Middle Polish phonology for more. – Labialization (ô, û – uo, uu) – Before ł vowels i and y pronounced like u, e.g. buł, zuł (był, żył).
• West-Masurian dialect (Działdowo, Nidzica, Szczytno) – Irregularly occurring á and labialization – Mni where Polish mi (mniasto, kamnień) – As in Ostróda district appear and have dominant position psi, bzi, (w)zi, f(si) to pchi, bhI etc. – Denasalization of the nasal vowels ą and ę as o and e.
• Center-Masurian dialect (Giżycko, Mrągowo, Pisz, Biała Piska) – The most common intermediate á – The most common archaic ř (in Polish sound as rż) – Frequent labialization – Appear and have dominant position pchi, bhI to psi, bzi etc. – Dominate pronunciation ni instead of mni – niasto, kanień etc. - Soft k, g, ch when is before a for example kia, gia, chia – Polish ą i ę like ón, on, én, en.
• East-Masurian dialect (Łek, Ôleck) – Polish ś, ć, ź pronounced like sz, cz, ż (for example spacz, bÿcz) – Á almost does not exist – a is frequently pronounced as a vowel intermediate between a and e (ä – mätkiä [ˈmætkʲæ], as in American English trap) – Synchronous pronunciation of soft labials b', p', f', w' change to bj, pj, fj, wj – Ch change to ś (kosianÿ, siätä) – Less frequent é and ó.
• North-Masurian dialect (Węgorzewo, Gołdap) – in the early 20th century almost disappeared, in the area Węgorzewa known for up to a few percent of the population (in the nineteenth century, more than half), in district of Gołdap 1% (in the nineteenth century, approx. 20%). – Very archaic sound for r – A relatively frequent á.

^[16][31]

• Dialects of the Polish language
• Languages of Europe
• Polish language
• Silesian language