Turkish (Türkçe [ˈtyɾktʃe], Türk dili, also known as Türkiye Türkçesi 'Turkish of Turkey') is the most widely spoken of the Turkic languages with around 90 million speakers. It is the national language of Turkey and one of two official languages of Cyprus. Significant smaller groups of Turkish speakers also exist in Germany, Austria, Bulgaria, North Macedonia, Greece, other parts of Europe, the South Caucasus, and some parts of Central Asia, Iraq, and Syria. Turkish is the 18th-most spoken language in the world.

To the west, the influence of Ottoman Turkish—the variety of the Turkish language that was used as the administrative and literary language of the Ottoman Empire—spread as the Ottoman Empire expanded. In 1928, as one of Atatürk's reforms in the early years of the Republic of Turkey, the Perso-Arabic script-based Ottoman Turkish alphabet was replaced with the Latin script-based Turkish alphabet.

Some distinctive characteristics of the Turkish language are vowel harmony and extensive agglutination. The basic word order of Turkish is subject–object–verb. Turkish has no noun classes or grammatical gender. The language makes usage of honorifics and has a strong T–V distinction which distinguishes varying levels of politeness, social distance, age, courtesy or familiarity toward the addressee. The plural second-person pronoun and verb forms can be used for referring to a single person out of respect.

Turkish is a member of the Oghuz group of the Turkic family. Other members include Azerbaijani, spoken in Azerbaijan and north-west Iran, Gagauz of Gagauzia, Qashqai of south Iran and the Turkmen of Turkmenistan.

Historically the Turkic family was seen as a branch of the larger Altaic family, including Japanese, Korean, Mongolian and Tungusic, with various other language families proposed for inclusion by linguists.

Altaic theory has fallen out of favour since the 1960s, and a majority of linguists now consider Turkic languages to be unrelated to any other language family, though the Altaic hypothesis still has a small degree of support from individual linguists. The nineteenth-century Ural-Altaic theory, which grouped Turkish with Finnish, Hungarian and Altaic languages, is considered even less plausible in light of Altaic's rejection. The theory was based mostly on the fact these languages share three features: agglutination, vowel harmony and lack of grammatical gender.

The earliest known Old Turkic inscriptions are the three monumental Orkhon inscriptions found in modern Mongolia. Erected in honour of the prince Kul Tigin and his brother Emperor Bilge Khagan, these date back to the Second Turkic Khaganate (dated 682–744 CE). After the discovery and excavation of these monuments and associated stone slabs by Russian archaeologists in the wider area surrounding the Orkhon Valley between 1889 and 1893, it became established that the language on the inscriptions was the Old Turkic language written using the Old Turkic alphabet, which has also been referred to as "Turkic runes" or "runiform" due to a superficial similarity to the Germanic runic alphabets.

With the Turkic expansion during Early Middle Ages (c. 6th–11th centuries), peoples speaking Turkic languages spread across Central Asia, covering a vast geographical region stretching from Siberia all the way to Europe and the Mediterranean. The Seljuqs of the Oghuz Turks, in particular, brought their language, Oghuz—the direct ancestor of today's Turkish language—into Anatolia during the 11th century. Also during the 11th century, an early linguist of the Turkic languages, Mahmud al-Kashgari from the Kara-Khanid Khanate, published the first comprehensive Turkic language dictionary and map of the geographical distribution of Turkic speakers in the Dīwān Lughāt al-Turk (ديوان لغات الترك).