Its usual name in English is jay (pronounced /ˈdʒeɪ/), with a now-uncommon variant jy /ˈdʒaɪ/.

[2][3] When used in the International Phonetic Alphabet for the voiced palatal approximant (the sound of "y" in "yes") it may be called yod or jod (pronounced /ˈjɒd/ or /ˈjoʊd/).

Middle English scribes began to use ⟨i⟩ (later ⟨j⟩) to represent word-initial /dʒ/ under the influence of Old French, which had a similarly pronounced phoneme deriving from Latin /j/ (for example, iest and later jest), while the same sound in other positions could be spelled as ⟨dg⟩ (for example, hedge).

In the Romance languages, ⟨j⟩ has generally developed from its original palatal approximant value in Latin to some kind of fricative.

In French, Portuguese, Catalan (except Valencian), and Romanian it has been fronted to the postalveolar fricative /ʒ/ (like ⟨s⟩ in English measure).

In Spanish, by contrast, it has been both devoiced and backed from an earlier /ʝ/ to a present-day /x/ or /h/,[10] with the actual phonetic realization depending on the speaker's dialect.

Until the 19th century, ⟨j⟩ was used instead of non-syllabic ⟨i⟩ in word-initial and intervocalic positions (as in Savoja) and as a replacement for final -ii; this rule was quite strict in official writing.

Some related languages, such as Serbo-Croatian and Macedonian, also adopted ⟨j⟩ into the Cyrillic alphabet for the same purpose.

In Basque, the diaphoneme represented by ⟨j⟩ has a variety of realizations according to the regional dialect: [j, ʝ, ɟ, ʒ, ʃ, x] (the last one is typical of Gipuzkoa).

Among non-European languages that have adopted the Latin script, ⟨j⟩ stands for /ʒ/ in Turkish and Azerbaijani, for /ʐ/ in Tatar, and for /dʒ/ in Indonesian, Somali, Malay, Igbo, Shona, Oromo, Turkmen, and Zulu.

Following Spanish usage, ⟨j⟩ represents [x] or similar sounds in many Latin-alphabet-based writing systems for indigenous languages of the Americas, such as [χ] in Mayan languages (ALMG alphabet) and a glottal fricative [h] in some spelling systems used for Aymara.

In Microsoft applications, ":)" is automatically replaced by a smiley rendered in a specific font face when composing rich text documents or HTML emails.