Once Upon a Time is an American fantasy adventure drama television series that aired for seven seasons on ABC from October 23, 2011, to May 18, 2018. The action alternates between two main settings: a fantastical world where fairy tales happen, and a fictional seaside town in Maine called Storybrooke. The "real-world" part of the story unfolds with the characters of Emma Swan (Jennifer Morrison) and her 10-year-old son, Henry Mills (Jared S. Gilmore). Henry discovers the other people of the town are fairy-tale characters. The audience is shown the backstory of the town's people as fairy-tale characters, in conjunction with their unfolding stories in the "real-world".

Once Upon a Time was created by Lost and Tron: Legacy writers Edward Kitsis and Adam Horowitz. The core themes of the show are hope and optimism. Horowitz told The Hollywood Reporter that they had a conscious purpose to "do a show that had optimism at its heart", as they "felt like there was so much darkness in the world". Kitsis said: "We are guys who like to see the world as half-full, not half-empty", and it's about "seeing that among all the trials and tribulations of life, you can persevere and find light among the darkness"; "it's that ability to think your life will get better".