The name Tajik, also spelled Tadzhik, refers to the Caucasoid people who represent the original Iranian population of present Afghanistan and the former Turkistan: the regions of Central Asian lying between Siberia on the north; Tibet, India, Afghanistan, and Iran on the south; the Gobi (desert) on the east; and the Caspian Sea on the west.

The Tajiks are the likely descendants of the Persian-speaking peoples that constitute the core of the ancient population of Khwarezm (Khorezm) and Bactria, which form part of Transoxania (Sogdiana).

Included in the empires of Persia and Alexander the Great, their presence in Central Asia and northern Afghanistan is attested from the middle of the first millennium BCE.

The Tajiks are the heirs and transmitters of the Central Asian sedentary culture that diffused in prehistoric times from the Iranian plateau into an area extending roughly from the Caspian Sea to the borders of China.