Achaeans or Achaean refers to the inhabitants or characteristics of the people of Achaea in Greece. However, the meaning of Achaea changed during the course of Ancient history, and thus, Achaeans/Achaean may mean:

In Greek mythology, the Trojan War was waged against the city of Troy by the Achaeans (Greeks) after Paris of Troy took Helen from her husband Menelaus king of Sparta. The war is one of the most important events in Greek mythology and has been narrated through many works of Greek literature, most notably through Homer's Iliad and the Odyssey. The Iliad relates a part of the last year of the siege of Troy; the Odyssey describes Odysseus's journey home. Other parts of the war are contained in a cycle of epic poems, which have survived through fragments. Episodes from the war provided material for Greek tragedy and other works of Greek literature, and for Roman poets including Virgil and Ovid.

The war originated from a quarrel between the goddesses Athena, Hera, and Aphrodite, after Eris, the goddess of strife and discord, gave them a golden apple, sometimes known as the Apple of Discord, marked "for the fairest". Zeus sent the goddesses to Paris, who judged that Aphrodite, as the "fairest", should receive the apple. In exchange, Aphrodite made Helen, the most beautiful of all women and wife of Menelaus, fall in love with Paris, who took her to Troy. Agamemnon, king of Mycenae and the brother of Helen's husband Menelaus, led an expedition of Achaean troops to Troy and besieged the city for ten years because of Paris' insult. After the deaths of many heroes, including the Achaeans Achilles and Ajax, and the Trojans Hector and Paris, the city fell to the ruse of the Trojan Horse. The Achaeans slaughtered the Trojans (except for some of the women and children whom they kept or sold as slaves) and desecrated the temples, thus earning the gods' wrath. Few of the Achaeans returned safely to their homes and many founded colonies in distant shores. The Romans later traced their origin to Aeneas, one of the Trojans, who was said to have led the surviving Trojans to modern day Italy.