The Ravens immediately improve their receiving attack around established veteran Anquan Boldin. Baltimore cut both receiver Derrick Mason and tight end Todd Heap last month.
"He's a quality veteran receiver who stretches the field and gives us significant downfield presence," Ravens general manager Ozzie Newsome said. "He's the type of person you want on your team. He brings leadership and maturity to the locker room."
Evans' best game last season came against the Ravens, when he had 105 yards receiving and three touchdowns in Buffalo's 37-34 overtime loss.
The Bills were not available for comment as they were traveling to Chicago in preparation for their preseason-opener.
The trade was not well received by at least one Bills veteran, cornerback Drayton Florence, who questioned the deal in several posts made on his Twitter account.
"Sad day for the bills," Florence wrote. "Are we trying to win now or later????"
Bills general manager Buddy Nix had previously sidestepped questions as to whether Evans was being shopped around.
Evans had been blindsided in reading reports of him being mentioned in trade talks. He eventually became resigned to being traded and informed several teammates of that likelihood after practice on Thursday, a person close to Evans told the AP. The second person also spoke on the condition of anonymity because Evans' conversations were considered private.
Selected by Buffalo in the first-round of the 2004 draft out of Wisconsin, Evans enjoyed two 1,000-yard seasons, but his numbers have tailed off over the past two years in part because of the Bills offensive struggles.
His best season came in 2006, when he had 82 catches for 1,292 yards and eight touchdowns.
Evans ranks third on the Bills' career list with 5,934 yards receiving. He's also fourth with 377 receptions and fifth with 43 touchdowns.
Evans is coming off his worst season. He had just 37 catches for 578 yards and four scores, while also missing the final three games with an ankle injury. Despite his sagging numbers, he still played a significant role in the Bills' passing attack by attracting coverage his way, which opened room for other receivers.
Evans was also a respected leader on the team, having been voted captain five times.
The trade allows the Bills to be second-guessed. Critics will question how this improves what's been an inconsistent offense for a team that's coming off a 4-12 season and missed the playoffs for an 11th year.
Despite showing modest gains on offense under quarterback Ryan Fitzpatrick last season, the Bills still finished 25th in yards gained and 28th in points scored. Buffalo scored more than 20 points only four times.
Without Evans, the Bills will proceed with a relatively untested group. It's a position that will now be led by Stevie Johnson, a fourth-year player, who's coming off a breakout season, and slot receiver Roscoe Parrish, a six-year veteran, who missed the final half of last season with a broken wrist.
Johnson led the Bills with 1,073 yards and 10 touchdowns last season.
Also in the group is David Nelson, who emerged as a third-down specialist last year. And then there's 2010 fourth-round draft pick Marcus Easley, who missed his entire rookie season with a knee injury. Easley had just resumed practicing this week after missing 10 days with a hyper-extended knee.
Also in the mix is Craig Davis, who is attempting to jump-start his career after four injury-troubled seasons with San Diego. A 2007 first-round draft pick, Davis signed with the Bills on Aug. 5.
