を, in hiragana, or ヲ in katakana, is one of the Japanese kana, each of which represents one mora.

Apart from some literate speakers who have revived [wo] as a spelling pronunciation[citation needed], though, this [w] sound is extinct in the modern spoken language.

[citation needed] In Romaji, the kana is transliterated variably as ⟨o⟩ or ⟨wo⟩, with the former being faithful to standard pronunciation, but the latter avoiding confusion with お and オ, and being in line with the structure of the gojūon.

Katakana ヲ can sometimes be combined with a dakuten, ヺ, to represent a /vo/ sound in foreign words; however, most IMEs lack a convenient way to do this as this usage has largely fallen into disuse.

Hiragana を is still used in several Okinawan orthographies for the mora /o~wo/; in the Ryukyu University system, it is /o/, whereas お is /ʔo/.