The A's received two right-handed pitchers -- Joey Devine, 24, and Minor Leaguer Jamie Richmond, 22 -- in exchange for Kotsay, 32, and a large chunk of his 2008 salary.
The move is the third in a series recently made by A's general manager Billy Beane, following the December trade of ace Dan Haren to the Diamondbacks in a deal that netted six prospects, and the trade of outfielder/first baseman Nick Swisher to the White Sox earlier this month for three prospects.
"With the transition taking place, I think the opportunity came to them from the Braves and their needs took over," Kotsay told MLB.com while waiting for a flight from Atlanta back home to the San Diego on Monday evening. "The prospects they got in return are good, and they got two arms, which seems to be the thing Billy's been looking for."
Kotsay, who missed the first two months of last season while recovering from lower-back surgery and missed the final six weeks of the season while on the disabled list with back spasms, passed his physical in Atlanta on Monday morning. The deal wasn't announced until late Monday afternoon because the amount of cash changing hands required approval from the Office of the Commissioner.
The final year of Kotsay's three-year contract calls for a salary of about $7 million and a $325,000 "relocation" bonus in the event of a trade, and the A's are said to be absorbing $5.325 million of that.
"Any time you're willing to pay a portion of the salary, it's because you like what you're getting back," A's assistant GM David Forst said in a conference call.
Forst added that Devine was so high on the club's Draft board in 2005 that he might have been its choice in the compensation round between the first and second rounds of that year's First-Year Player Draft had he not already been selected. The A's instead used the pick on Travis Buck, who saw his rookie season in 2007 cut short by injuries but will enter Spring Training as the outfielder with the most service time in Oakland.
Devine has appeared sparingly for the Braves in each of the past three seasons, allowing only one run in 10 appearances last season. Richmond, who turns 23 in March, began his pro career as a reliever in 2005 but has primarily started the past two seasons. His cumulative work in the Atlanta system shows a record of 16-7 with a 2.48 ERA.
Kotsay, an 11-year veteran who also has played for the Marlins and Padres, said he appreciated the opportunity to reestablish himself with a contending team after consecutive injury marred seasons.
"To me, this is kind of like it was for me when I came to Oakland [in a 2003 trade from the Padres]," he explained. "I was coming off some back problems then, and the Braves put me through the same kind of physical that the A's did. But Oakland wanted me then, and the Braves want me now. That's what I needed, and I'm thankful Billy sent me to a place like Atlanta."
Added Forst, "Mark is one of the best guys we've had around here, and to some extent you try to look out for those guys and find an opportunity that works out for everybody. This was kind of the best of both worlds. I think it's a good situation for Mark."
Kotsay said he wasn't surprised that the A's were looking to deal him before Spring Training, noting that it would have been a gamble to wait for him to get healthy enough to possibly command a greater return package in a midsummer swap.
"I don't think Billy wanted to risk it and go through the variable of me having a setback," Kotsay explained. "Billy's too smart for that. If my back went out, he'd have been stuck with a big salary for nothing.
In his first year with the A's, Kotsay formed a friendship with pitcher Tim Hudson, who was traded to the Braves after the 2004 season. Hudson remains one of the leaders of the Atlanta pitching staff.
"Huddy's awesome," Kotsay said. "Our wives get along, we get along, and our kids are about the same ages, so that's another thing that's really nice about this. At least there's some familiarity."
The trade, actually struck Saturday pending the physical by Kotsay, who was limited to 56 games last season by lower-back problems, was anticipated in the wake of Beane's prior decisions to deal Haren and Swisher.
And, suggested Forst, the A's might not be done dealing.
"We are in that same position of fielding phone calls," Forst said. We're working on other things, with three arbitration-eligible players [Joe Blanton, Chad Gaudin and Huston Street] and the filing date for arbitration coming Friday. There are some other free-agent opportunities we're looking at, too.
"This doesn't change anything. We're still essentially fielding phone calls."
Before hopping onto his flight home, Kotsay was told that A's owner Lew Wolff recently was quoted as saying he felt the A's, despite their recent youth movement, would be a competitive club in 2007. Kotsay didn't disagree.
"I wouldn't give up hope if I was an A's fan," he said. "Billy's a competitor. He's always going to want to win, and I don't think going toward a younger team right now changes that. So I don't think Lew's wrong at all. He believes in Billy, and so should A's fans.
"The possibility of being competitive is there. Obviously they'll need some things to go their way, but Billy knows what he's doing. I think A's fans would be crazy to jump ship, to be honest. I really do."
Mychael Urban is a national writer for MLB.com. Tom Singer of MLB.com contributed to this report. This story was not subject to the approval of Major League Baseball or its clubs.