Marshallese (Marshallese: Kajin Ṃajeḷ or Kajin Majōl [kɑzʲinʲ(i)mˠɑːzʲɛlˠ]), also known as Ebon, is a Micronesian language spoken in the Marshall Islands. The language of the Marshallese people, it is spoken by nearly all of the country's population of 59,000, making it the principal language. There are also roughly 27,000 Marshallese citizens residing in the United States, nearly all of whom speak Marshallese, as well as residents in other countries such as Nauru and Kiribati.

There are two major dialects, the western Rālik and the eastern Ratak.

Marshallese, a Micronesian language, is a member of the Eastern Oceanic subgroup of the Austronesian languages. The closest linguistic relatives of Marshallese are the other Micronesian languages, including Gilbertese, Nauruan, Pohnpeian, Mokilese, Chuukese, Refaluwasch, and Kosraean. Marshallese shows 50% lexical similarity with Gilbertese, Mokilese, and Pohnpeian.

Within the Micronesian archipelago, Marshallese—along with the rest of the Micronesian language group—is not as closely related to the more ambiguously classified Oceanic language Yapese in Yap State, or to the Polynesian outlier languages Kapingamarangi and Nukuoro in Pohnpei State, and even less closely related to the non-Oceanic languages Palauan in Palau and Chamorro in the Mariana Islands.

The Republic of the Marshall Islands contains 34 atolls that are split into two chains, the eastern Ratak Chain and the western Rālik Chain. These two chains have different dialects, which differ mainly lexically, and are mutually intelligible. The atoll of Ujelang in the west was reported to have "slightly less homogeneous speech", but it has been uninhabited since 1980.

The Ratak and Rālik dialects differ phonetically in how they deal with stems that begin with double consonants. Ratak Marshallese inserts a vowel to separate the consonants, while Ralik adds a vowel before the consonants (and pronounced an unwritten consonant phoneme /j/ before the vowel). For example, the stem kkure 'play' becomes ikkure in Rālik Marshallese and kukure in Ratak Marshallese.

Marshallese is the official language of the Marshall Islands and enjoys vigorous use. As of 1979, the language was spoken by 43,900 people in the Marshall Islands. in 2020 the number was closer to 59,000. Additional groups of speakers in other countries including Nauru and the United States increase the total number of Marshallese speakers, with approximately 27,000 Marshallese-Americans living in the United States. Along with Pohnpeian and Chuukese, Marshallese stands out among Micronesian languages in having tens of thousands of speakers; most Micronesian languages have far fewer. A dictionary and at least two Bible translations have been published in Marshallese.

Marshallese has a large consonant inventory, and each consonant has some type of secondary articulation (palatalization, velarization, or rounding). The palatalized consonants are regarded as "light", and the velarized and rounded consonants are regarded as "heavy", with the rounded consonants being both velarized and labialized. (This contrast is similar to that between "slender" and "broad" consonants in Goidelic languages, or between "soft" and "hard" consonants in Slavic languages.) The "light" consonants are considered more relaxed articulations.