In phonetics, nasalization (or nasalisation) is the production of a sound while the velum is lowered, so that some air escapes through the nose during the production of the sound by the mouth. An archetypal nasal sound is [n].

In the International Phonetic Alphabet, nasalization is indicated by printing a tilde diacritic U+0303 ◌̃ COMBINING TILDE above the symbol for the sound to be nasalized: [ã] is the nasalized equivalent of [a], and [ṽ] is the nasalized equivalent of [v]. A subscript diacritic [ą], called an ogonek or nosinė, is sometimes seen, especially when the vowel bears tone marks that would interfere with the superscript tilde. For example, [ą̄ ą́ ą̀ ą̂ ą̌] are more legible in most fonts than [ã̄ ã́ ã̀ ã̂ ã̌].