The ʻokina, also called by several other names, is a unicameral consonant letter used within the Latin script to mark the phonemic glottal stop, as it is used in many Polynesian languages.

The ʻokina visually resembles a left single quotation mark (‘)—a small "6"-shaped mark above the baseline.

The Tahitian ʻeta has a distinct shape, like an ʻokina turned 90° or more clockwise.

The ʻokina is a letter in the Hawaiian alphabet. It is unicameral—that is, it does not have separate uppercase (capital) and lowercase ("small") forms—unlike the other letters, all of which are basic Latin letters. For words that begin with an ʻokina, capitalization rules affect the next letter instead: for instance, at the beginning of a sentence, the name of the letter is written "ʻOkina", with a capital O.

The United States Board on Geographic Names lists relevant place names both with and without the ʻokina and kahakō (macron) in the Geographic Names Information System. Colloquially and formally, the forms have long been used interchangeably.^[4]

In the ASCII character set, the ʻokina is typically represented by the apostrophe character ('), ASCII value 39 in decimal and 27 in hexadecimal. This character is typically rendered as a straight typewriter apostrophe, lacking the curve of the ʻokina proper. In some fonts, the ASCII apostrophe is rendered as a right single quotation mark, which is an even less satisfactory glyph for the ʻokina—essentially a 180° rotation of the correct shape.

Many other character sets expanded on the overloaded ASCII apostrophe, providing distinct characters for the left and right single quotation marks.

The left single quotation mark has been used as an acceptable approximation to the ʻokina, though it still has problems: the ʻokina is a letter, not a punctuation mark, which may cause incorrect behaviour in automated text processing. Additionally, the left single quotation mark is represented in some typefaces by a mirrored "9" glyph, rather than a "6", which is unsuitable for the ʻokina.

In the Unicode standard, the ʻokina is encoded as U+02BB ʻ MODIFIER LETTER TURNED COMMA, which can be rendered in HTML by the entity ʻ (or in hexadecimal form ʻ).^[1]

Although this letter was introduced in Unicode 1.1 (1993), lack of support for this character prevented easy and universal use for many years.

As of 2008, OS X, Microsoft Windows and Linux-based computers and all new major smartphones have no problem with the glyph, and it is no longer a problem in Internet Explorer 7 as it was in previous versions. U+02BB should be the value used in encoding new data when the expected use of the data permits.

The same character is sometimes used in Latin transliterations of the Hebrew letter ʻáyin and the Arabic letter ʻayn (which is not a glottal stop) as well as in the Uzbek alphabet to write the letters Oʻ (Cyrillic Ў) and Gʻ (Cyrillic Ғ). However, "ʻokina" and other Polynesian names are properly reserved for the glottal stop in Polynesian language orthographies. Other glottal stop characters, such as U+02C0 ˀ MODIFIER LETTER GLOTTAL STOP, are inappropriate for the ʻokina.

The distinct form of the Tahitian and Wallisian glottal stop is not currently assigned a separate character in Unicode.