The Emerald City is the capital city of the Land of Oz and the domain of its Wizard in The Wizard of Oz. It can be reached from Munchkin Country via the Yellow Brick Road and is centrally located between Oz's Northern, Southern, Eastern, and Western territories.
In Return to Oz, the Emerald City is in ruins, its residents turned to stone by the Nome King, and ruled by Mombi and her Wheelers.
In The Muppets' Wizard of Oz, its residents include Sam the Eagle as the Gate Guard, Scooter as Assistant to the Wizard, and Dr. Bunsen Honeydew and Beaker as its technicians.
In Oz the Great and Powerful, Evanora the Wicked Witch of the East and the Wicked Witch of the West had taken over the Emerald City and used it as their personal headquarters. The residents lived unaware of their rulers' tyranny until they discovered the truth and attempted to rebel against them. After Oscar Diggs becomes the Wizard of Oz and drives the two witches out of Emerald City, Glinda the Good Witch of the South reclaims her rightful place as ruler of the Emerald City, with Oscar ruling by her side.
In the ABC series Once Upon a Time, the Emerald City is where Zelena was raised.