Sogdia (/ˈsɒɡdiə/) or Sogdiana was an ancient Iranian civilization between the Amu Darya and the Syr Darya rivers, and in present-day Uzbekistan, Turkmenistan, Tajikistan, Kazakhstan, and Kyrgyzstan. Sogdiana was also a province of the Achaemenid Empire, and listed on the Behistun Inscription of Darius the Great. Sogdiana was first conquered by Cyrus the Great, the founder of the Achaemenid Empire, and then was annexed by the Macedonian ruler Alexander the Great in 328 BC. It would continue to change hands under the Seleucid Empire, the Greco-Bactrian Kingdom, the Kushan Empire, the Sasanian Empire, the Hephthalite Empire, the Western Turkic Khaganate, and the Muslim conquest of Transoxiana.

The Sogdian city-states, although never politically united, were centered on the city of Samarkand. Sogdian, an Eastern Iranian language, is no longer spoken. However, a descendant of one of its dialects, Yaghnobi, is still spoken by the Yaghnobis of Tajikistan. It was widely spoken in Central Asia as a lingua franca and served as one of the First Turkic Khaganate's court languages for writing documents.

Sogdians also lived in Imperial China and rose to prominence in the military and government of the Chinese Tang dynasty (618–907 AD). Sogdian merchants and diplomats travelled as far west as the Byzantine Empire. They played an essential part as middlemen in the Silk Road trade route. While initially practicing the faiths of Zoroastrianism, Manichaeism, Buddhism and, to a lesser extent, the Church of the East from West Asia, the gradual conversion to Islam among the Sogdians and their descendants began with the Muslim conquest of Transoxiana in the 8th century. The Sogdian conversion to Islam was virtually complete by the end of the Samanid Empire in 999, coinciding with the decline of the Sogdian language, as it was largely supplanted by New Persian.

Sogdiana lay north of Bactria, east of Khwarezm, and southeast of Kangju between the Oxus (Amu Darya) and the Jaxartes (Syr Darya), including the fertile valley of the Zeravshan (called the Polytimetus by the ancient Greeks). Sogdian territory corresponds to the modern regions of Samarkand and Bukhara in modern Uzbekistan, as well as the Sughd region of modern Tajikistan. In the High Middle Ages, Sogdian cities included sites stretching towards Issyk Kul, such as that at the archeological site of Suyab.

Oswald Szemerényi devotes a thorough discussion to the etymologies of ancient ethnic words for the Scythians in his work Four Old Iranian Ethnic Names: Scythian – Skudra – Sogdian – Saka. In it, the names provided by the Greek historian Herodotus and the names of his title, except Saka, as well as many other words for "Scythian", such as Assyrian Aškuz and Greek Skuthēs, descend from *skeud-, an ancient Indo-European root meaning "propel, shoot" (cf. English shoot). *skud- is the zero-grade; that is, a variant in which the -e- is not present. The restored Scythian name is *Skuδa (archer), which among the Pontic or Royal Scythians became *Skula, in which the δ has been regularly replaced by an l. According to Szemerényi, Sogdiana (Old Persian: Suguda-; Persian: سغد, romanized: Soġd; Tajik: Суғд, سغد, romanized: Suġd; Chinese: 粟特; Greek: Σογδιανή, romanized: Sogdianē) was named from the Skuδa form. Starting from the names of the province given in Old Persian inscriptions, Sugda and Suguda, and the knowledge derived from Middle Sogdian that Old Persian -gd- applied to Sogdian was pronounced as voiced fricatives, -γδ-, Szemerényi arrives at *Suγδa as an Old Sogdian endonym. Applying sound changes apparent in other Sogdian words and inherent in Indo-European, he traces the development of *Suγδa from Skuδa, "archer", as follows: Skuδa > *Sukuda by anaptyxis > *Sukuδa > *Sukδa (syncope) > *Suγδa (assimilation).

Sogdiana possessed a Bronze Age urban culture: original Bronze Age towns appear in the archaeological record beginning with the settlement at Sarazm, Tajikistan, spanning as far back as the 4th millennium BC, and then at Kök Tepe, near modern-day Bulungur, Uzbekistan, from at least the 15th century BC.

In the Avesta, namely in the Mihr Yasht and the Vendidad, the toponym of Gava (gava-, gāum) is mentioned as the land of the Sogdians. Gava is, therefore, interpreted as referring to Sogdia during the time of the Avesta. Although there is no universal consensus on the chronology of the Avesta, most scholars today argue for an early chronology, which would place the composition of Young Avestan texts like the Mihr Yasht and the Vendiad in the first half of the first millennium BCE.

The first mention of Gava is found in the Mihr Yasht, ie., the hymn dedicated to the Zoroastrian deity Mithra. In verse 10.14 it is described how Mithra reaches Mount Hara and looks at the entirety of the Airyoshayan (airiio.shaiianem, 'lands of the Arya'),