Gemination of consonants is distinctive in some languages and then is subject to various phonological constraints that depend on the language.

In Berber, each consonant has a geminate counterpart, and gemination is lexically contrastive. The distinction between single and geminate consonants is attested in medial position as well as in absolute initial and final positions.

In some dialects gemination is also found for some words when the suffix -ly follows a root ending in -l or -ll, as in:

In French, gemination is usually not phonologically relevant and therefore does not allow words to be distinguished: it mostly corresponds to an accent of insistence ("c'est terrifiant" realised [ˈtɛʁ.ʁi.fjɑ̃]), or meets hyper-correction criteria: one "corrects" one's pronunciation, despite the usual phonology, to be closer to a realization that one imagines to be more correct: thus, the word illusion is sometimes pronounced [il.lyˈzjɔ̃] by influence of the spelling.

In Norwegian, gemination is indicated in writing by double consonants. Gemination often differentiates between unrelated words. As in Italian, Norwegian uses short vowels before doubled consonants and long vowels before single consonants. There are qualitative differences between short and long vowels:

In Polish, consonant length is indicated with two identical letters. Examples:

Consonant length is distinctive and sometimes is necessary to distinguish words:

Double consonants are common on morpheme borders where the initial or final sound of the suffix is the same as the final or initial sound of the stem (depending on the position of the suffix). Examples:

Gemination is specially characteristic of Punjabi compared to other Indo-Aryan languages like Hindi-Urdu, where instead of the presence of consonant lengthening, the preceding vowel tends to be lengthened. Consonant length is distinctive in Punjabi, for example:

In Turkish gemination is indicated by two identical letters as in most languages that have phonemic gemination.

Loanwords originally ending with a phonemic geminated consonant are always written and pronounced without the ending gemination as in Arabic.

Gemination also occurs when a suffix starting with a consonant comes after a word that ends with the same consonant.

Doubled orthographic consonants do not always indicate a long phonetic consonant.