In exchange, the Red Sox sent infielder/outfielder Yamaico Navarro, who had been on the Major League roster since June 30, and Kendal Volz, a 23-year-old pitching prospect, to the Royals.
Aviles, 30, has played mostly second and third base in 53 games this season, with some time at shortstop as well. In the Majors this year, he's hitting .222 with a .261 on-base percentage and five home runs in 185 at-bats. He finished fourth in the 2008 Rookie of the Year voting.
He arrived at U.S. Cellular Field about the third inning of Saturday night's game against the White Sox, and was given uniform No. 3.
"I got woken up by a phone call and I have to go to the field and find out that I got traded," Aviles said. "It's definitely a good thing. I thank Kansas City for the opportunity, and I'm excited to be here and be part of what's going on here and help out in any way I can."
Aviles can help the Red Sox with his versatility, his baserunning and ability to hit lefties.
"He's a guy I think our organization has kind of liked from afar for a while," said Red Sox manager Terry Francona. "He came up -- he was that guy that could really hit left-handers -- actually both."
Aviles can roam around the infield, with plenty of experience at second, short and third.
It is fair to wonder how he fits once Jed Lowrie returns from a left shoulder injury, which could be in about a week.
However, Francona said the club might try to get Aviles comfortable in the outfield, though it's unclear if that would happen before Spring Training.
"Some of it is probably going to depend on Jed because Jed's probably not too far away. But [Aviles] seems excited to be here. We're happy to have him. At some point, I think we'd like to get him to the outfield just because I think we think he can do it. He hasn't done that yet, but we'll see."
Aviles has confidence he could hold his own in the outfield, a position he last played in college.
"I know I'm pretty athletic, so I know I can pick it up pretty quick," Aviles said.
Though Aviles has struggled in the Majors this season, he performed well at Triple-A, hitting .307 with a .329 OBP and a .586 slugging percentage in 35 games, with nine home runs. He played 34 of those games at shortstop.
Aviles, a native of New York, was drafted by the Royals in the seventh round of the First-Year Player Draft in 2003, and debuted in the Majors in 2008. In the two Major League seasons in which he's finished with 400 at-bats, '08 and '10, Aviles has hit over .300.
Hailing from the Dominican Republic, Navarro had been a part of the Red Sox organization since 2005. He made his Major League debut last year and has a lifetime .177 (14-for-79) average in 36 career big league games.
Navarro's first career homer was on July 1 at Houston, and it was as a pinch-hitter.
"I think it's probably good for him because I think he'll get a chance to probably play more there than he would here," Francona said. "We certainly wish him well."
At High Class A Salem, Volz went 2-3 with two saves and a 3.33 ERA with 56 strikeouts and 12 walks in 31 appearances this season. He ranks third among Carolina League relievers with a 9.82 strikeouts per nine innings. He was a ninth-round Draft pick of the Sox in 2009, and is 8-8 with a 3.60 ERA in 167 2/3 career innings in pro ball.
Francona indicated that the addition of Aviles was something that was also made with an eye toward next year, likening it to the deal that brought Jarrod Saltalmacchia to Boston a year ago.
"I was pretty surprised," Aviles said. "I didn't think anything was in the works. I didn't know. It's a good surprise, in that case, to come to a team that's a perennial winning team and always has a chance to be in the playoffs and win a World Series, and I'm fortunate enough to be part of that right now."