"O"-Jung.Ban.Hap., sometimes referred to as "O"-Union or just O, is the third Korean studio album by South Korean boy group TVXQ, released through SM Entertainment on September 29, 2006. In a year when Korean music sales had slumped, it was the highest selling album in South Korea in 2006 and won the group several prominent awards in South Korea. The album stayed charted within the top 50 throughout 2007, and sold over 480,000 copies in South Korea by 2022.

TVXQ, known as Tohoshinki in Japan, is a South Korean pop duo formed by SM Entertainment, composed of U-Know Yunho and Max Changmin.