The Seleucid era ("SE") or Anno Graecorum, sometimes denoted "AG," was a system of numbering years in use by the Seleucid Empire and other countries among the ancient Hellenistic civilizations, and later by the Parthians. It is sometimes referred to as "the dominion of the Seleucidæ," or the Year of Alexander. The era dates from Seleucus I Nicator's reconquest of Babylon in 312/11 BC after his exile in Ptolemaic Egypt, considered by Seleucus and his court to mark the founding of the Seleucid Empire. According to Jewish tradition, it was during the sixth year of Alexander the Great's reign that they began to make use of this counting. The introduction of the new era is mentioned in one of the Babylonian Chronicles, the Chronicle of the Diadochi.

The Seleucid Empire was a Greek power in West Asia during the Hellenistic period. It was founded in 312 BC by the Macedonian general Seleucus I Nicator, following the division of the Macedonian Empire founded by Alexander the Great, and ruled by the Seleucid dynasty until its annexation by the Roman Republic under Pompey in 63 BC.