During a Captain America storyline, the super soldier serum running through Steve Rogers' veins was neutralised rendering the WWII hero an old man. Sam Wilson picks up the shield and takes on the mantle maintaining his wings in the process. Sam was a member of the Mighty Avengers (Vol. 2) under Luke Cage's leadership. If the title of this comic is to be believed, it would appear that "Falcon" is taking over this branch of the Avengers.
Meanwhile, Spider-Man has been kicked off from the team following his Superior Spider-Man problems.
But that doesn't stop him from getting dragged back for a guest appearance in most of the issues in this title.