Fita (Ѳ, ѳ) is a letter of the early Cyrillic alphabet, descended from the Greek Theta. It was mainly used to write proper names derived from Greek. SinceRussians would pronounce these names with an /f/ sound instead of the proper sound /θ/ (which is like English unvoiced "th")—for example "Theodore" would be pronounced as "Feodor"—it was replaced in Russian by the letter Ef (Ф, ф) in 1918. In most other Slavic languages (as well as a few rare Greek words in Russian with phth, such as фталевая кислота, "phthalic acid"), Fita was pronounced /t/ and was replaced with Te, e.g. the Bulgarian and Serbian version of Theodore is Тодор or Теодор, romanized Todor or Teodor.

As thita, it is also used in the Romanian Cyrillic alphabet, used until about 1860.

Fita is not to be confused with the similar-looking Cyrillic letter barred o (Ө, ө), which is currently used in the Kazakh, Tuvan, and Mongolian languages.