Ionians a branch of the ancient Greeks. The Ionians were originally from eastern Greece. They, the Arcadians, and the Aeolians were descended from the Achaeans, who entered Greece and founded the Mycenaean civilization between 2000 and 1700 B.C. Most Ionians fled to Asia Minor after the Dorian invasion about 1100 B.C. The west coast of Asia Minor and the islands of Samos and Chios became known as Ionia. There were 12 Ionian cities; the leading ones were Miletus and Ephesus.

Ionia was a center of Greek culture before the Classic Age in Greece. The philosopher-scientists Thales, Pythagoras, and Heraclitus were Ionians. Ionia became wealthy from trade and established many colonies on the coasts of the Black Sea and the Mediterranean Sea.

Ionia was conquered by the Lydians in the 560's B.C. and by the Persians in the 540's. Athenian efforts to help Ionia regain independence were one of the causes of the Persian Wars, 490–479 B.C.