For the article on Æ, the Irish writer, see: George William Russell

"Æ", or "æ", is a vowel and a grapheme used in the Icelandic, Danish, Faroese, and Norwegian alphabets. It was also used in Old English and in medieval and early modern Latin. Modern English still contains several words that use æ, such as Encyclopædia, but it is falling into disuse. The origin of the letter is a ligature for AE.

In Icelandic, the letter Æ signifies a diphthong (IPA ). The same goes in Faroese for the so-called long Æ (IPA [ɛa]), whereas the short Æ is a simple [a]. In Danish and Norwegian, Æ represents a simple vowel, namely IPA [ɛ] and [æ], respectively. The same phoneme is represented in Swedish by the letter "Ä", and in German by "A-Umlaut" (written Ä).

In Old English, the æ ligature was used to denote a sound intermediate between those of "A" and "E" (IPA [æ]), very much like the short "A" of cat in many dialects of modern English. In this context, the name of the letter is Æsc (Ash in modern English, meaning the tree), after the name of the corresponding rune in the Anglo-Saxon Futhorc related to the Older Futhark As rune.

In Classical Latin, the combination denotes a diphthong (IPA [ae̯]) that had a value similar to the long "I" in most dialects of modern English. It was used both in native words (spelled with "AI" before the 2nd century BC) and in borrowings from Greek words having the diphthong "AI" ("ΑΙ"). Both classical and modern practice is to write the letters separately, but the ligature was used in medieval and early modern writings, in part because "Æ" was reduced to a simple long vowel (IPA [eː]) in late Latin. In some medieval scripts, the ligature was simplified to an "e-caudata", the letter e with a "tail" hanging to the left: ę. This form further simplified into a normal 'e', which may have influenced or been influenced by the pronunciation change.

The symbol [æ] is also used in the International Phonetic Alphabet to denote the sound of the Old English letter, a near-open front unrounded vowel, as in the modern English word cat. In this context, it is always lowercase.

For computers, when using the Latin-1 or Unicode sets, the codes for 'Æ' and 'æ' are respectively 0198 and 0230 (holding down the ALT key whilst typing in 0198 on the number pad will produce the character on Windows systems and holding down the option or alt key (⌥) whilst typing an apostrophe (') on a United States Macintosh keyboard), or C6 and E6 in hexadecimal. In HTML, the HTML character entity references Æ and æ have been assigned to Æ and æ, respectively.

The progressive metal band Tool used an Æ for the title of their third album, Ænima, and the song Ænema off of that album. This is similar to the usage of the heavy metal umlaut, but is meant as a combination of anima and enema.

In addition, the British electronic music group Autechre sometimes abbreviate their name to æ, as can be seen, for example, on the cover of their single, Gantz Graf.