The Seleucid Empire (/sɪˈljuːsɪd/;Ancient Greek: Βασιλεία τῶν Σελευκιδῶν, Basileía tōn Seleukidōn) was a Hellenistic state ruled by the Seleucid dynasty, which existed from 312 BC to 63 BC; it was founded by Seleucus I Nicator following the division of the Macedonian empire created by Alexander the Great. Seleucus received Babylonia and, from there, expanded his dominions to include much of Alexander's near eastern territories. At the height of its power, it included central Anatolia, Persia, the Levant, Mesopotamia, and what is now Kuwait, Afghanistan, and parts of Pakistan and Turkmenistan.

The Seleucid Empire was a major center of Hellenistic culture that maintained the preeminence of Greek customs where a Greek political elite dominated, mostly in the urban areas. The Greek population of the cities who formed the dominant elite were reinforced by immigration from Greece. Seleucid expansion into Anatolia and Greece was abruptly halted after decisive defeats at the hands of the Roman army. Their attempts to defeat their old enemy Ptolemaic Egypt were frustrated by Roman demands. Having come into conflict with Chandragupta Maurya of the Maurya Empire, after several defeats, Seleucus entered into an agreement with Chandragupta Maurya where he ceded vast territory west of the Indus, including the Hindu Kush, modern day Afghanistan, and the Balochistan province of Pakistan and offered his daughter for marriage to the Emperor to formalize the alliance. Much of the eastern part of the empire was conquered by the Parthians under Mithridates I of Parthia in the mid-2nd century BC, yet the Seleucid kings continued to rule a rump state from Syria until the invasion by Armenian king Tigranes the Great and their ultimate overthrow by the Roman general Pompey.