"O"-Jung.Ban.Hap.

"O"-Jung.Ban.Hap. (stylized as "O"-正.反.合.), sometimes referred to as "O"-Union or just O, is the third Korean studio album (fourth overall) 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.

The album's name "O"-Jung.Ban.Hap, literally translated to "O"-Justice.Opposition.Solution, is based on Georg Wilhelm Friedrich Hegel's theory of thesis, antithesis, synthesis. The album's lead single of the same name has lyrics that regard global conflicts with a plea for peace and resistance. The album contains a balance of fast tempo songs and ballads.