"Sometimes you've got to let your good people go to pursue what they need to pursue to make themselves happy," Celtics President Rich Gotham said. "While it's tough to see Doc go, I think we feel good about what he did here. We will be lucky to find as good a coach as Doc was."
Los Angeles also spoke to Boston about acquiring star forward Kevin Garnett in another element of the trade involving Rivers, but NBA Commissioner David Stern won't allow teams to trade active players for a coach.
Garnett and Southern California native Paul Pierce won't be reuniting with Rivers in Los Angeles any time soon: Ainge said the NBA has forbidden player trades between the two teams for the rest of the year, and both aging stars are under contract for next season. Garnett has discussed the possibility of retirement with two years and over $23.5 million left on his deal, while Pierce is due to make $15.3 million next season.
Rivers played one season for the Clippers in 1991-92 during his 13-year NBA career, and they made the playoffs that season for the first time since the former Buffalo Braves moved to the West Coast in 1978. Los Angeles has made only five playoff appearances and won just two rounds since that season.
But the Clippers are coming off the best two-season stretch in club history, and Rivers' arrival further alters the franchise's decades-long reputation.
Rivers will be an intriguing match with the high-flying Clippers and their Lob City acrobatics, but his coaching pedigree and leadership skills will provide him with immediate credibility in his new locker room.
Rivers' Boston teams played at a more deliberate pace than last season's Clippers often used last season, but the veteran coach is likely to adapt his offensive plans to fit the Clippers' talent. Rivers' impact on Los Angeles could be felt most on defense, where the Clippers often struggled last season despite their lofty record.
After his playing career ended in 1996, Rivers went into broadcasting before serving as the Orlando Magic's head coach for just over four seasons from 1999-2003, going 171-168 and winning an NBA coach of the year award. He is one of four active NBA coaches who have won a championship.
AP Sports Writer Jimmy Golen in Boston contributed to this report.