There have been rumours for a while now (especially since the Sony hacking scandal) that Marvel and Sony had been trying to work out a deal to bring spider-Man into the Marvel Cinematic Universe. It turns out that the rumours are true. It is happening. And it is happening in both directions.
From Marvel's press release:
Spider-Man is set to have his first stand-alone MCU movie in 2017, which means that his first appearance will likely be in Captain America: Civil War. I can only imagine how difficult it was for the two companies to make that deal, but the timing couldn't have been better to have him as part of the Civil War storyline. As Sony said in the press release; "This is the right decision for the franchise, for our business, for Marvel, and for the fans."
Agreed. As a fan, I could not be happier. If Marvel's announcement of their future roadmap wasn't exciting enough, it sure is now.