Proto-Polynesian (abbreviated PPn) is the reconstructed proto-language from which all modern Polynesian languages descend. It is a descendant of the Proto-Oceanic language (the language associated with the Lapita civilization), itself a descendant of Proto-Austronesian. The homeland of Proto-Polynesian speakers is believed to have been Tonga, Samoa, and nearby islands.

Proto-Polynesian has a small phonological inventory, with 13 consonants and 5 vowels.

Proto-Polynesian had five vowels, /a/ /e/ /i/ /o/ /u/, with no length distinction. In a number of daughter languages, successive sequences of vowels came together to produce long vowels and diphthongs, and in some languages these sounds later became phonemic.

The following is a table of some sample vocabulary as it is represented orthographically in various languages. All instances of ⟨ʻ⟩ represent a glottal stop, IPA /ʔ/. All instances of ⟨ng⟩ and Samoan ⟨g⟩ represent the single phoneme /ŋ/. The letter ⟨r⟩ in all cases represents voiced alveolar tap /ɾ/, not /r/.