The Letoon trilingual, or Xanthos trilingual, is an inscription in three languages: standard Lycian or Lycian A, Greek, and Aramaic covering the faces of a four-sided stone stele called the Letoon Trilingual Stele, discovered in 1973 during the archeological exploration of the Letoon temple complex, near Xanthos, ancient Lycia, in present-day Turkey. It was created when Lycia was under the sway of the Persian Achaemenid Empire. The inscription is a public record of a decree authorizing the establishment of a cult, with references to the deities, and provisions for officers in the new cult. The Lycian requires 41 lines; the Greek, 35 and the Aramaic, 27. They are not word-for-word translations, but each contains some information not present in the others. The Aramaic is somewhat condensed.

Lycia was a historical region in Anatolia from 15–14th centuries BC to 546 BC. It bordered the Mediterranean Sea in what is today the provinces of Antalya and Muğla in Turkey as well some inland parts of Burdur Province. The region was known to history from the Late Bronze Age records of ancient Egypt and the Hittite Empire.