Sidetic is a member of the extinct Anatolian branch of the Indo-European language family. It is known from legends of coins, found in Side at the Pamphylian coast, that date to the period of approximately the 5th to 3rd centuries BCE, and from two Greek–Sidetic bilingual inscriptions from the 3rd and 2nd centuries BCE. The Greek historian Arrian in his Anabasis Alexandri (mid-2nd century CE) mentions the existence of a peculiar indigenous language in the city of Side, which is assumed to be the language of the coins and inscriptions. Sidetic was probably closely related to Lydian, Carian and Lycian.

Sidetic was written with a script of the Anatolian group. The Sidetic alphabet has 31 identified letters, a few of which are clearly derived from Greek. The script has been partially deciphered, though the phonetic values of many letters are uncertain.

Coins from Side were first discovered in the 19th century, which bore legends in a then-unknown script. In 1914, an altar came to light in Side with a Greek inscription and a Sidetic one, but the latter could not be deciphered. It was only after the discovery of a second Greek-Sidetic bilingual inscription in 1949, that Hellmut Theodor Bossert was able to identify 14 letters of the Sidetic script using the two bilinguals. In 1964 a large stone block was unearthed near the east gate of Side, with two longer Sidetic texts, including loan words from Greek (istratag from στρατηγός, 'commander' and anathema- from ἀνάθημα, 'votive offering'). In 1972, a text was found outside Side for the first time, at the neighbouring town of Lyrbe-Seleukia. Currently, eleven Sidetic coins and several coins with Sidetic legends are known.

In addition to the inscriptions, two Sidetic words are known from ancient Greek texts: ζειγάρη for cicada, mentioned by the ancient lexicographer Hesychius, and λαέρκινον for Valeriana, cited by Galen. In addition, it is believed that some incomprehensible characters in the third book of Hippocrates' Epidemics were originally quotations of the doctor Mnemon of Side, which might have been in the Sidetic script.

The designated number and date of discovery are given:

In addition a few Sidetic words have been handed down via classical authors, though not written in Sidetic script: "laerkinon" (λαέρκινον, = the herb valerian), "zeigarê" (ζειγάρη, a cricket, cicada).

Texts in the Sidetic language are written right to left in an alphabet of 31 distinct letters in inscriptions, plus another 4 characters found only on coins. Recent research is providing updates to the script: there are new letters and variants

The values of two-thirds of the letters are now firmly established, but there are still significant uncertainties: for example, while the majority view is that the frequent vertical strokes ( or ) are a character denoting a sibilant (z or s), that as a genitival ending would fit in nicely with the usual paradigms of the Anatolian languages, others interpret the strokes as word dividers.