Star Butterfly is a magical princess from the dimension of Mewni. On her 14th birthday, she receives the family heirloom wand. After she accidentally sets fire to her castle, her parents decide that a safer option is to send her to Earth as a foreign exchange student. She befriends Marco Diaz and lives with his family while attending Echo Creek Academy. Star and Marco must deal with everyday school life while protecting Star's wand from falling into the hands of Ludo, a villain from Mewni who commands an army of monsters. Star and the folks from Mewni are able to travel across dimensions using "dimensional scissors" that can open portals.
After having skirmished with a number of dangerous monsters on her home planet of Mooney, Star Butterfly arrives on Earth to live with the Diaz family. However, rather than living a normal life, Star, with Marco Diaz, continues to battle villains throughout the universe and in their high school, mainly to protect her extremely powerful wand, an object that she is still yet to master.