Unbreakable is the sixth studio album (fifth in the United States) by American group Backstreet Boys. It was released on October 24, 2007 in Japan, followed by a worldwide release. The album marked the group's first release as a quartet, following Kevin Richardson's departure in 2006 to pursue other interests. It was also their first album without the involvement of longtime collaborators Max Martin and Kristian Lundin, who had worked on all of the group’s previous albums, with Dan Muckala assuming a larger role in the album's production.