The Elvish script used for the One Ring inscription in J.R.R. Tolkien’s works is Tengwar. Tolkien designed Tengwar as a writing system rather than a spoken language, and it can represent several languages in Middle-earth.
The Ring inscription is written in Tengwar characters, but the words themselves are in the Black Speech of Mordor. This distinction is important: Tengwar identifies the script, while Black Speech identifies the language of the inscription.
Tengwar was created by the fictional Fëanor and is associated particularly with the Elves. Tolkien also invented the Cirth, a separate runic writing system used in different cultural and historical contexts. Modern fans often use Tengwar for decorative inscriptions, though Tolkien’s spelling conventions vary by language.