Shushtar (Persian: شوشتر) is a city in the Central District of Shushtar County, Khuzestan province, Iran, serving as capital of both the county and the district.

Shushtar is an ancient fortress city, approximately 92 kilometres (57 mi) from Ahvaz, the centre of the province. Much of its past agricultural productivity derives from the irrigation system which centered on the Band-e Kaisar, the first dam bridge in Iran. The whole water system in Shushtar consists of 13 sites called Shushtar Historical Hydraulic System which is registered as a Unesco World Heritage Site.

In the Elamite times Shushtar was known as Adamdun.^{[citation needed]} In the Achaemenian times its name was Šurkutir.^{[citation needed]} According to tradition, Shushtar was founded by the legendary king Hushang after he built Susa (aka Shush), and the name "Shushtar" was a comparative form meaning "more beautiful than Shush". Josef Marquart also interpreted the name Shushtar as being derived from Shush, but with a slightly different meaning, with the suffix "-tar" indicating a direction. The Arabic name of the city, Tustar, is an adaptation of the Persian form Shushtar.

Shushtar may be the "Sostra" mentioned by Pliny the Elder. It is also known in Syriac literature as a Nestorian bishopric.

During the Sassanian era, it was an island city on the Karun river and selected to become the summer capital. The river was channeled to form a moat around the city, while bridges and main gates into Shushtar were built to the east, west, and south. Several rivers nearby are conducive to the extension of agriculture; the cultivation of sugar cane, the main crop, dates back to 226. A system of subterranean channels called Ghanats, which connected the river to the private reservoirs of houses and buildings, supplied water for domestic use and irrigation, as well as to store and supply water during times of war when the main gates were closed. Traces of these ghanats can still be found in the crypts of some houses.

Under the caliphate, Shushtar was the capital of one of the seven kuwar (sub-provinces) that made up Khuzestan. Its kurah likely encompassed the eastern edge of the northern Khuzestan plain. Today, this area is inhabited by semi-nomadic people, and only lightly - which possibly explains why al-Maqdisi wrote that he "[knew] no towns" that were dependencies of Shushtar.

Historically, Shushtar was always one of the most important textile-producing cities in Khuzestan. Authors throughout the Middle Ages consistently listed a diverse array of textile products manufactured at Shushtar. For example, al-Istakhri (writing c. 933) listed dibaj (brocade) and tiraz; al-Maqdisi (writing c. 1000) listed dibaj, anmat (carpets), cotton, and Merv-style clothes; and Hafiz-i Abru (writing c. 1430) recorded dibaj, tiraz, and harir (silk). Shushtar's commercial importance was recognized by its being chosen to produce the Kiswah (the embroidered covering for the Kaaba) in 933 — a major honor with political importance.

According to al-Maqdisi's account, there was a cemetery right in the middle of Shushtar. Nanette Marie Pyne says that this is "not as unusual a phenomenon as it sounds: cemeteries in this part of Iran are often placed on the highest ground, in some places to avoid the raised water table, in others to avoid taking cultivable land out of production." In the case of Shushtar, the highest ground would have been in the middle of the city, on top of the settlement mound formed by Parthian and Sasanian occupation. Al-Maqdisi also describes that Shushtar's mosque was located "in the middle of the markets in the cloth merchants' area." A second cloth market was located by the city gate. The cloth fullers' area was located by the bridge, which was nearby.