Teos or Teo was an ancient Greek city on the coast of Ionia, on a peninsula between Chytrium and Myonnesus. It was founded by Minyans from Orchomenus, Ionians and Boeotians, but the date of its foundation is unknown. Teos was one of the twelve cities which formed the Ionian League. The city was situated on a low hilly isthmus. Its ruins are located to the south of the modern town of Sığacık in the Seferihisar district of Izmir Province, Turkey.

Ionia was an ancient region on the western coast of Anatolia, to the south of present-day İzmir, Turkey. It consisted of the northernmost territories of the Ionian League of Greek settlements. Never a unified state, it was named after the Ionians who had settled in the region before the archaic period.