The Indo-Iranian languages, also referred to as Indo-Iranic languages or collectively as the Aryan languages, represent the most extensive and southeastern branch within the Indo-European language family. This linguistic group encompasses over 300 distinct languages, spoken by approximately 1.5 billion individuals primarily across South Asia, West Asia, and certain parts of Central Asia.

Classification of Indo-Iranian Languages
Within the broader Indo-European family, the Indo-Iranian languages constitute the easternmost major branch, with only the Tocharian languages extending further eastward. Scholarly consensus predominantly recognizes two primary subgroups within the Indo-Iranian languages, namely the Iranian and Indo-Aryan language groups. Some scholars also propose the inclusion of Nuristani and Bangani languages within the Indo-Iranian category.

Etymology of Indo-Iranian Language
The term "Indo-Iranian languages" encompasses the spectrum of Indo-European languages spoken across Southern Asia, ranging from the Indian subcontinent (Indic branch or Indo-Aryan) to the Iranian Plateau (Iranian branch). Historically, these languages were associated with the ethnocultural self-designation of ancient Indo-Iranians as "Aryan languages." However, contemporary scholarly discourse veers away from the term "Aryan" due to its connotations and associations, particularly following World War II.

History of Indo-Iranian Languages
The hypothetical common ancestor of all Indo-Iranian languages is Proto-Indo-Iranian, also known as Common Aryan. It is believed to have been spoken around the late 3rd millennium BC in the Eurasian steppe region bordering the Ural River to the west, the Tian Shan to the east, and Transoxiana and the Hindu Kush to the south. The Indo-Iranian languages branch into three primary groups: Indo-Aryan, Iranian, and Nuristani. Previous scholarship proposed a fourth independent branch, Dardic, which recent research generally places within the Indo-Aryan branch.

Geographical Distribution of Indo-Iranian Languages
Indo-Iranian languages are dispersed across diverse geographical regions, extending from Europe and the Caucasus to Mesopotamia, Iran, Xinjiang, Assam, Sri Lanka, and the Maldives. Additionally, branches of these languages are found in Oceania and the Caribbean, with significant diaspora communities present in northwestern Europe, North America, Australia, South Africa, and the Persian Gulf region.

Diversity of Indo-Iranian languages
There are approximately more than 300 distinct Indo-Iranian languages, according to scholars. Among these languages, Hindustani, encompassing both Hindi and Urdu, boasts the highest number of native speakers within the Indo-Iranian language family.
In the early 21st century, nearly one billion individuals were speakers of Indo-Iranian languages, primarily residing across southwestern and southern Asia. Modern Iranian languages, with a speaker count ranging between 150 and 200 million, include Persian, Pashto, and Kurdish as the most widely spoken among them. On the other hand, modern Indo-Aryan languages count more than 800 million speakers, with Hindi, Bengali, Marathi, and Urdu being the most prevalent.
Among the Indo-European languages, only Greek and Hittite possess written records older than those of Indo-Iranian. These languages have played significant roles in administrative and literary contexts throughout history. Old Persian served as the administrative language during the early Achaemenian dynasty, dating back to the 6th century BCE. Similarly, an eastern Middle Indo-Aryan dialect was used in the chancellery of Mauryan emperor Asoka in the Indian subcontinent during the mid-3rd century BCE.

Influence of Indo-Iranian Languages
Moreover, Indo-Iranian languages have left indelible marks on the literature of several major world religions. Indo-Aryan languages, for instance, have been instrumental in the scriptures of Buddhism, Hinduism, Jainism, and Sikhism. Meanwhile, Iranian languages have played pivotal roles in the religious texts of Zoroastrianism and Manichaeism, with the oldest Zoroastrian texts being in dialects included under the name Avestan.
The influence of these languages has transcended geographical boundaries, facilitated by commerce, conquest, and religious propagation. Indo-Aryan languages, for instance, spread into Southeast Asia, leaving lexical borrowings in Indonesia, Thailand, and other regions. Additionally, Sanskrit texts in Cambodia stand as enduring evidence of this linguistic influence, showcasing the profound impact of Indo-Iranian languages on global cultural heritage.
Understanding the Indo-Iranian languages provides invaluable insights into the linguistic, historical, and cultural tapestry of South Asia, West Asia, and beyond. With its rich diversity and historical significance, this linguistic branch continues to intrigue scholars and enthusiasts alike.