In phonetics, palatalization or palatalisation (/ˌpælətəlaɪˈzeɪʃən/ ^ⓘ, US also /-lɪ-/) is a way of pronouncing a consonant in which part of the tongue is moved close to the hard palate. Consonants pronounced this way are said to be palatalized and are transcribed in the International Phonetic Alphabet by affixing a superscript j ⟨ʲ⟩ to the base consonant. Palatalization is not phonemic in English, but it is in Slavic languages such as Russian and Ukrainian, Finnic languages such as Estonian, Karelian, and Võro, and other languages such as Irish, Marshallese, Kashmiri, and Japanese.

In technical terms, palatalization refers to the secondary articulation of consonants by which the body of the tongue is raised toward the hard palate and the alveolar ridge during the articulation of the consonant. Such consonants are phonetically palatalized. "Pure" palatalization is a modification to the articulation of a consonant, where the middle of the tongue is raised, and nothing else. It may produce a laminal articulation of otherwise apical consonants such as /t/ and /s/.

Phonetically palatalized consonants may vary in their exact realization. Some languages add semivowels before or after the palatalized consonant (onglides or offglides). In such cases, the vowel (especially a non-front vowel) following a palatalized consonant typically has a palatal onglide. In Russian, both plain and palatalized consonant phonemes are found in words like большой [bɐlʲˈʂoj] ^ⓘ, царь [tsarʲ] ^ⓘ and Катя [ˈkatʲə] ^ⓘ. In Hupa, on the other hand, the palatalization is heard as both an onglide and an offglide. In some cases, the realization of palatalization may change without any corresponding phonemic change. For example, according to Thurneysen, palatalized consonants at the end of a syllable in Old Irish had a corresponding onglide (reflected as ⟨i⟩ in the spelling), which was no longer present in Middle Irish (based on explicit testimony of grammarians of the time).

In a few languages, including Skolt Sami and many of the Central Chadic languages, palatalization is a suprasegmental feature that affects the pronunciation of an entire syllable, and it may cause certain vowels to be pronounced more front and consonants to be slightly palatalized. In Skolt Sami and its relatives (Kildin Sami and Ter Sami), suprasegmental palatalization contrasts with segmental palatal articulation (palatal consonants).

In the International Phonetic Alphabet (IPA), palatalized consonants are marked by the modifier letter ⟨ʲ⟩, a superscript version of the symbol for the palatal approximant ⟨j⟩. For instance, ⟨tʲ⟩ represents the palatalized form of the voiceless alveolar stop [t]. Prior to 1989, a subscript diacritic was used in the IPA: ⟨ᶀ ᶈ ᶆ ᶂ ᶌ ƫ ᶁ ᶇ ᶊ ᶎ ᶅ 𝼓 ᶉ 𝼖 𝼕 ᶄ ᶃ 𝼔 ᶍ ꞕ⟩, apart from two palatalized fricatives which were written instead with curly-tailed variants, namely ⟨ʆ⟩ for [ʃʲ] and ⟨ʓ⟩ for [ʒʲ]. (See palatal hook.) The Uralic Phonetic Alphabet marks palatalized consonants by an acute accent, as do some Finnic languages using the Latin alphabet, as in Võro ⟨ś⟩. Others use an apostrophe, as in Karelian ⟨s'⟩; or digraphs in j, as in the Savonian dialects of Finnish, ⟨sj⟩.

Palatalization has varying phonological significance in different languages. It is allophonic in English, but phonemic in others. In English, consonants are palatalized when they occur before front vowels or the palatal approximant (and in a few other cases), but no words are distinguished by palatalization (complementary distribution), whereas in some of the other languages, the difference between palatalized consonants and plain un-palatalized consonants distinguishes between words, appearing in a contrastive distribution (where one of the two versions, palatalized or not, appears in the same environment as the other).

In some languages, like Hindustani, palatalization is allophonic. Some phonemes have palatalized allophones in certain contexts, typically before front vowels and unpalatalized allophones elsewhere. Because it is allophonic, palatalization of this type does not distinguish words and often goes unnoticed by native speakers. Phonetic palatalization occurs in American English. Stops are palatalized before the front vowel /i/ and not palatalized in other cases.

In some languages, palatalization is a distinctive feature that distinguishes two consonant phonemes. This feature occurs in Russian, Irish, and Scottish Gaelic, among others.