The fifth season of the American ABC fantasy-drama Once Upon a Time was ordered on May 7, 2015. It began airing on September 27, 2015, and ended on May 15, 2016. On June 9, 2015, the promotion of Rebecca Mader and Sean Maguire to series regulars was announced for the fifth season, portraying their characters Zelena / Wicked Witch of the West and Robin Hood, respectively, while a few days later, Michael Socha was confirmed to not be returning as a series regular as Will Scarlet / Knave of Hearts. The fifth season also saw the series reach its 100th episode, which aired on March 6, 2016 as the mid-season premiere.
New characters introduced to the series during the season include King Arthur, Guinevere, Merlin, Merida, Percival, Nimue, Hades, Hercules, Megara, Zeus, Poole, Jekyll and Hyde. The season also saw the return of numerous deceased characters from the first four seasons, including the Blind Witch, Queen of Hearts, Peter Pan, Cruella De Vil, Baelfire/Neal Cassidy, Milah, Prince Henry, Liam Jones, Prince James, Gaston, Claude and Stealthy.