In Iran despite the massive embracing of Persian language, the number of Azerbaijani Turkish speakers has increased since the 1950s. Based on a field work carried in Tehran and Salmas, the author identifies the present situation as a diglossia because the speakers lean to use Turkish in the private space and Persian in the public space. This diglossia has been institutionalised by the Islamic Republic, with an official distinction between Persian and the regional languages (including Turkish): The former is recognised as the official and national language in the Constitution. Recently, through literary publications or other cultural activities, and through the ever-growing impact of Anatolian Turkish, Azerbaijani Turkish has started to be used in areas formerly restricted to Persian language. Consequently, the author assumes a progressive normalisation of Azerbaijani Turkish in Iran. So doing, he offers a decisive contribution in his field, casting light on the current strengthening of ethnic and regional identification in Iran.