Although there is a high degree of mutual intelligibility between both forms of Azerbaijani, there are significant differences in phonology, lexicon, morphology, syntax, and sources of loanwords.

Azerbaijani is closely related to Turkmen, Turkish, Gagauz, and Qashqai, being mutually intelligible with each of these languages to varying degrees.

In the early years following the establishment of the Azerbaijan Soviet Socialist Republic, the language was still referred to as "Turkic" in official documents.

Early Azerbaijani differs from its descendant in that it contained a much larger number of Persian and Arabic loanwords, phrases and syntactic elements.

Early writings in Azerbaijani also demonstrate linguistic interchangeability between Oghuz and Kypchak elements in many aspects (such as pronouns, case endings, participles, etc.).

As Azerbaijani gradually moved from being merely a language of epic and lyric poetry to being also a language of journalism and scientific research, its literary version has become more or less unified and simplified with the loss of many archaic Turkic elements, stilted Iranisms and Ottomanisms, and other words, expressions, and rules that failed to gain popularity among the Azerbaijani masses.

[16][17] Between c. 1900 and 1930, there were several competing approaches to the unification of the national language in what is now the Azerbaijan Republic, popularized by scholars such as Hasan bey Zardabi and Mammad agha Shahtakhtinski.

They all criticized the overuse of Persian, Arabic, and European elements in both colloquial and literary language and called for a simpler and more popular style.

[20][21] Kadi Burhan al-Din, Hasanoghlu, and Imadaddin Nasimi helped to establish Azerbaiijani as a literary language in the 14th century through poetry and other works.

[21] One ruler of the Qara Qoyunlu state, Jahanshah, wrote poems in Azerbaijani language with the nickname "Haqiqi".

[24] The ruler and poet Ismail I wrote under the pen name Khatā'ī (which means "sinner" in Persian) during the fifteenth century.

[8][25] During the 16th century, the poet, writer and thinker Fuzûlî wrote mainly in Azerbaijani but also translated his poems into Arabic and Persian.

His most important work is Heydar Babaya Salam and it is considered to be a pinnacle of Azerbaijani literature and gained popularity in the Turkic-speaking world.

An Azerbaijani koine served as a lingua franca throughout most parts of Transcaucasia except the Black Sea coast, in southern Dagestan,[27][28][29] the Eastern Anatolia Region and all over Iran[30] from the 16th to the early 20th centuries,[31][32] alongside cultural, administrative, court literature, and most importantly official language (along with Azerbaijani) of all these regions, namely Persian.

[35] Linguists Mohammad Salehi and Aydin Neysani write that "there is a high degree of mutual intelligibility" between North and South Azerbaijani.

[35] Svante Cornell wrote in his 2001 book Small Nations and Great Powers that "it is certain that Russian and Iranian words (sic), respectively, have entered the vocabulary on either side of the Araxes river, but this has not occurred to an extent that it could pose difficulties for communication".

[39] Ethnologue lists 21 North Azerbaijani dialects: "Quba, Derbend, Baku, Shamakhi, Salyan, Lenkaran, Qazakh, Airym, Borcala, Terekeme, Qyzylbash, Nukha, Zaqatala (Mugaly), Qabala, Nakhchivan, Ordubad, Ganja, Shusha (Karabakh), Karapapak, Kutkashen, Kuba".

The CIA World Factbook reports that in 2010, the percentage of Iranian Azerbaijani speakers was at around 16 percent of the Iranian population, or approximately 13 million people worldwide,[44] and ethnic Azeris form by far the second largest ethnic group of Iran, thus making the language also the second most spoken language in the nation.

[61] This is observed in the Turkmen literary language as well, where the demonstrative pronoun bu undergoes some changes just as in: munuñ, munı, muña, munda, mundan, munça.

[77] Despite this, the number and even the existence of diphthongs in Azerbaijani has been disputed, with some linguists, such as Abdulazal Damirchizade [az], arguing that they are non-phonemic.

In Iran, the process of standardization of orthography started with the publication of Azerbaijani magazines and newspapers such as Varlıq (وارلیق — Existence) from 1979.

Azerbaijani-speaking scholars and literarians showed great interest in involvement in such ventures and in working towards the development of a standard writing system.

These effort culminated in language seminars being held in Tehran, chaired by the founder of Varlıq, Javad Heyat, in 2001 where a document outlining the standard orthography and writing conventions were published for the public.

[84] For instance, until an Aliyev decree on the matter in 2001,[85] newspapers would routinely write headlines in the Latin script, leaving the stories in Cyrillic.

[citation needed] Some samples include: Secular: Invoking deity: Azerbaijani has informal and formal ways of saying things.