Algiz (also Elhaz) is the name conventionally given to the "z-rune" ᛉ of the Elder Futhark runic alphabet. Its transliteration is z, understood as a phoneme of the Proto-Germanic language, the terminal *z continuing Proto-Indo-European terminal *s.

It is one of two runes which express a phoneme that does not occur word-initially, and thus could not be named acrophonically, the other being the ŋ-rune Ingwaz ᛜ. As the terminal *-z phoneme marks the nominative singular desinence of masculine nouns, the rune occurs comparatively frequently in early epigraphy.

Because this specific phoneme was lost at an early time, the Elder Futhark rune underwent changes in the medieval runic alphabets. In the Anglo-Saxon futhorc it retained its shape, but it was given the sound value of Latin x. This is a secondary development, possibly due to runic manuscript tradition, and there is no known instance of the rune being used in an Old English inscription.

In Proto-Norse and Old Norse, the Germanic *z phoneme developed into an R sound, perhaps realized as a retroflex approximant [ɻ], which is usually transcribed as ʀ. This sound was written in the Younger Futhark using the Yr rune ᛦ, the Algiz rune turned upside down, from about the 7th century. This phoneme eventually became indistinguishable from the regular R sound in the later stages of Old Norse, at about the 11th or 12th century.