Blue Letter (EP)

Blue Letter is the second extended play by the South Korean singer Wonho. It was released on September 14, 2021 by Highline Entertainment and distributed by Kakao Entertainment. Wonho was involved in the writing and production of all tracks in the EP, alongside contributors including Enan, Sun Ahn, Savage House Gang, and Oshimaxx. Musically, the EP consists primarily of pop songs, with elements of dance and R&B.

To promote Blue Letter, Wonho released the single "Blue" alongside the EP and held a promotional concert titled We Are Young, which took place on November 2021 in Seoul. He also made several appearances on South Korean music shows, performing the EP's lead single and select album tracks.

The EP peaked at number 5 on South Korea's Circle Album Chart and has sold over 70,000 copies in the country. Internationally, it reached number 86 on the Billboard Japan Top Download Albums chart. The lead single "Blue" charted on digital download charts in both South Korea and the United States.