The Red Sox acquired infielder Mike Aviles from the Royals for infielder/outfielder Yamaico Navarro and reliever Kendal Volz, according to the Royals' official Twitter feed.
Aviles, 30, has struggled this year, getting demoted in June, but owns a career line of .286/.317/.417 in 1218 plate appearances. He finished fourth in the Rookie of the Year voting in 2008, and is capable of playing second base, shortstop, and third base. He'll be arbitration eligible for the first time after the season and is under team control through 2014.
Navarro, 23, hit .258/.362/.469 in 149 Triple-A plate appearances this year, playing all over the diamond. Prior to the season, Baseball America ranked Navarro 12th among Red Sox prospects, citing 15-20 home run potential but questioning his maturity. Volz, 23, posted a 3.33 ERA, 9.8 K/9, 2.1 BB/9, and 1.1 HR/9 in 51 1/3 relief innings at High-A this year and is not among the team's top 30.