Moon Haewon (혜원; birth name 문혜원, Moon Hae-won) is a South Korean jazz vocalist who records under the name MOON. Her releases print the name in several ways: "Moon" on her first album, "MOON haewon" on Apple Music and on the Japanese issues, "Moon Haewon" on later singles, and "Haewon Moon" on Spotify and as the main entry on Discogs. Korean press writes it Moon(혜원) or simply 혜원. She was born on November 15, 1984, according to Korean Wikipedia, Wikidata and MusicBrainz, which agree; none of them gives a birthplace, and Wikidata lists South Korean citizenship. She is 41.

The Korean music service Genie, introducing her solo debut in 2018, says she came to music through her family, prepared early to become a singer and met jazz at school. Korean Wikipedia records a bachelor's degree in applied music (생활음악) at Dankook University and coursework toward a master's degree in popular music at its graduate school of culture and the arts. It also says she sang as a guest vocalist with the Sonagi Project in 2007. She first reached a wide audience in 2008 as the singer of Winterplay, the pop-jazz project led by the trumpeter Juhan Lee. Their debut album Choco Snow Ball came out on January 23, 2008, and its single "Happy Bubble" became the theme of a washing-machine advertisement. Korean Wikipedia files the Winterplay albums from Choco Snow Ball (2008) to Two Fabulous Fools (2013) under her own discography, and the Discogs notes for Hot Summerplay (2009) name Moon Hye-won as the vocalist. In 2010 she sang with the group in London, at the Korean Cultural Centre among other places, as London Korean Links recalled in 2019, and Genie says the work earned a gold disc in Korea and a best vocalist title from the magazine Jazz People. Korean Wikipedia and Genie both place her departure in 2016.

Her break from the group began in Japan. In March 2017 a television programme on TBS, Sawako no Asa, featured Winterplay's Songs of Colored Love (2009), and according to the Kyunghyang newspaper the eight-year-old album then climbed to number one on the Amazon and iTunes jazz charts in Japan. A year later she released her solo debut, Kiss Me, under the new stage name Moon. It came out on February 7, 2018 in Japan and Hong Kong and in Korea on March 12, on the Verve label through Universal Music, which Korean newspapers described as unusual for a Korean musician: the album was made and released in Japan first, and they presented it as the first Verve release by a musician from Korea. It was produced by the guitarist Goro Ito of the Brazilian-music duo Naomi & Goro, and the singer-flugelhorn player TOKU appears on "Something Stupid". The title track, a pop song first recorded by Sixpence None the Richer, reached number one on the iTunes jazz chart in Japan, and concerts were scheduled in Korea, Hong Kong and Japan that spring. Korean Wikipedia adds that the album topped a Hong Kong pop chart.

A second Verve album, Tenderly, followed on July 10, 2019. London Korean Links described it as a sister piece to Kiss Me, recorded in Japan with an all-Japanese ensemble. Chromatic Paradise (2021) and Beyond the Moon (2023) came next, each on Universal Music and each preceded by singles. Korean Wikipedia says that since her solo debut she has written lyrics, composed and produced as well as sung.

In 2024 she began a partnership with the pianist Tsuyoshi Yamamoto, a veteran of Japanese jazz. Midnight Sun (Somethin' Cool, April 24, 2024), recorded in Tokyo on November 27 and 28, 2023 with Yamamoto's trio, mixes standards such as "Autumn Leaves", "Misty" and "Send in the Clowns" with her own song "Look to the Moon". The Japanese magazine Jazz Critique chose it as the best vocal album of 2024 in its Jazz Audio Disc Awards, as the Kyunghyang newspaper reported in March 2025. The follow-up Fascination (Somethin' Cool, October 1, 2025) was recorded in Tokyo on April 16 and 17, 2025, and in March 2026 the same magazine gave it the Gold Award in the vocal category, her second in a row. Two 10-inch records, Holiday Gift from Moon (2024) and Love Songs from Moon (January 21, 2026), complete the series. Her fifth solo album, Paper Wing, was released on June 23, 2026, following a single of the same name on May 21.

There is no published account of a jazz teacher or mentor, and no source gives her birthplace.

Her solo records are built on standards and well-known songs, sung in a clear, light voice with little ornament. Kyunghyang quoted the Jazz Critique reviewer Seiichi Goto saying that Midnight Sun showed sophisticated, happy music and a sensitive collaboration, an album he wanted to hear many times. Kiss Me mixes Latin and bossa nova arrangements ("Brazasia", "Quando, Quando, Quando", "Speak Low") with pop ("Kiss Me", "Private Eyes") and a Japanese song that Korean listeners know in Nami's version as 슬픈 인연. Tenderly reworks pieces by George Gershwin, the Corrs, Green Day, Minnie Riperton and Burt Bacharach, in the words of London Korean Links, with "Walk On By" sung over a lightly thundering arrangement. The two Yamamoto albums are piano-trio jazz: standards, ballads and a few songs she wrote.

Her early work with Winterplay was lighter. Genie, writing in 2018, contrasted that "lighter, prettier" feel with the depth and elegance of the solo albums, and the Winterplay records are filed under pop as often as under jazz, so some of her public profile comes from pop-jazz and from television and advertising music. Her solo career has been jazz throughout: Discogs tags Kiss Me as jazz, the album prizes she has won are jazz awards, and her recent collaborator is one of Japan's most respected jazz pianists. Audiences in Japan, Hong Kong and Thailand have been the most responsive, Korean Wikipedia says.