Indo-Iranian Languages, group of related languages spoken by more than 500 million people in a region extending from eastern Turkey to Bangladesh and including most of India. The Indo-Iranian languages form the largest subfamily (296 languages) of the Indo-European languages.

The Indo-Iranian languages are generally divided into an Iranian branch; an Indic, or Indo-Aryan, branch; and an Unclassified group of two languages. Major Iranian languages include ancient Avestan and Old Persian, various medieval languages, modern Persian, Pashto or Afghan, Kurdish languages, and Baluchi languages. They are spoken by more than 60 million people. Also of Iranian stock are the languages of the ancient Scythians and Sarmatians and a modern remnant, Ossetic, or Osetin (see Ossetians), spoken in the Caucasus. The Indo-Aryan branch, consisting of 210 languages spoken by some 500 million people in the northern and central parts of the Indian subcontinent, includes the ancient Sanskrit language; Indian medieval languages that developed from Sanskrit called Prakrits (including Pali); and modern languages such as Hindi, Urdu, Bangla, Gujarati, and other Indian languages, Nepali (official in Nepal and Sikkim), and Sinhalese (official in Sri Lanka). Considered to be an Indo-Aryan sub-group are the Dardic languages, which include Kashmiri and Shina.

Early Sanskrit literature is the oldest of any Indo-European literature except Hittite. Sanskrit and Avestan resemble each other closely and are considered to reflect extremely faithfully the consonantal system and elaborate inflections of the Proto-Indo-European language. The modern Indic and Iranian branches have tended to simplify the ancient consonantal system and to replace inflections with word combinations. The Indo-Aryan languages were also influenced by the sounds and grammar of the non-Indo-European Dravidian language family.

Selected statistical data from Ethnologue: Languages of the World, SIL International.