A glottal stop or glottal plosive is a type of consonantal sound used in many spoken languages, produced by obstructing airflow in the vocal tract or, more precisely, the glottis. The symbol in the International Phonetic Alphabet that represents this sound is ⟨ʔ⟩.

As a result of the airflow in the glottis, the glottal vibration either stops or becomes irregular with a low rate and sudden drop in intensity.

Features of a glottal stop:

In the traditional romanization of many languages, such as Arabic, a glottal stop is transcribed with the apostrophe ⟨ʼ⟩ or the symbol ⟨ʾ⟩, which is the source of the IPA character ⟨ʔ⟩. In many Polynesian languages that use the Latin alphabet, however, the glottal stop is written with a rotated apostrophe, ⟨ʻ⟩ (called ʻokina in Hawaiian and Samoan), which is commonly used to transcribe the Arabic ayin as well (also ⟨ʽ⟩) and is the source of the IPA character for the voiced pharyngeal fricative ⟨ʕ⟩. In Malay the glottal stop is represented by the letter ⟨k⟩ (at the end of words), in Võro and Maltese by ⟨q⟩. Another way of writing the glottal stop is the saltillo ⟨Ꞌ ꞌ⟩, used in languages such as Tlapanec and Rapa Nui.

Other scripts also have letters used for representing glottal stops, such as the Hebrew letter aleph ⟨א‎⟩ and the Cyrillic letter palochka ⟨Ӏ⟩, used in several Caucasian languages. The Arabic script uses hamza ⟨ء⟩, which can appear both as a diacritic and as an independent letter (though not part of the alphabet). In Tundra Nenets, it is represented by the letters apostrophe ⟨ʼ⟩ and double apostrophe ⟨ˮ⟩. In Japanese, glottal stops occur at the end of interjections of surprise or anger and are represented by the character ⟨っ⟩.

In the graphic representation of most Philippine languages, glottal stops have no consistent symbolization. In most cases, however, a word that begins with a vowel-letter (e.g. Tagalog aso, "dog") is always pronounced with an unrepresented glottal stop before that vowel (as in Modern German and Hausa). Some orthographies use a hyphen instead of the reverse apostrophe if the glottal stop occurs in the middle of the word (e.g. Tagalog pag-ibig, "love"; or Visayan gabi-i, "night"). If it occurs in the end of a word, the last vowel can be written with a circumflex accent (known as the pakupyâ) if both a stress and a glottal stop occur in the final vowel (e.g. basâ, "wet") or a grave accent (known as the paiwà) if the glottal stop occurs at the final vowel, but the stress occurs at the penultimate syllable (e.g. batà, "child").

Some Canadian indigenous languages, especially some of the Salishan languages, have adopted the IPA letter ⟨ʔ⟩ into their orthographies. In some of them, it occurs as a casing pair, ⟨Ɂ⟩ and ⟨ɂ⟩. The digit ⟨7⟩ or a question mark is sometimes substituted for ⟨ʔ⟩, and is preferred in languages such as Squamish. SENĆOŦEN – whose alphabet is mostly unique from other Salish languages – contrastly uses the comma ⟨,⟩ to represent the glottal stop, though it is optional.

In 2015, two women in the Northwest Territories challenged the territorial government over its refusal to permit them to use the letter ⟨ʔ⟩ in their daughters' names: Sahaiʔa, a Chipewyan name, and Sakaeʔah, a Slavey name (the two names are actually cognates). The territory argued that territorial and federal identity documents were unable to accommodate the character. The women registered the names with hyphens instead of the ⟨ʔ⟩, while continuing to challenge the policy.