Scarlett Ingrid Johansson was born in the Manhattan borough of New York City. Her father, Karsten Olaf Johansson, is an architect originally from Copenhagen, Denmark, and her paternal grandfather, Ejner Johansson, was an art historian, screenwriter and film director, whose own father was Swedish. Scarlett's mother, Melanie Sloan, a producer, comes from an Ashkenazi Jewish family, from Poland and Russia. She has an older sister, Vanessa, also an actress; an older brother, Adrian; and a twin brother, Hunter. Johansson also has an older half-brother, Christian, from her father's first marriage. She holds both American and Danish citizenship. The actress is a maternal great-niece of Phil Schlamberg, the last known combat death of World War II, who was the wingman to Captain Jerry Yellin.
Johansson attended PS 41, an elementary school in Greenwich Village, Manhattan. Her parents divorced when she was 13. Johansson was particularly close to her maternal grandmother, Dorothy Sloan, a bookkeeper and schoolteacher; they often spent time together and Johansson considered Sloan her best friend. Interested in a career in the spotlight from an early age, she often put on song-and-dance routines for her family. She was particularly fond of musical theater and jazz hands. She took lessons in tap dance, and states that her parents were supportive of her career choice. She describes her childhood as very ordinary.
As a child, Johansson practiced acting by staring in the mirror until she made herself cry, wanting to be Judy Garland in Meet Me in St. Louis. At age seven, she was devastated when a talent agent signed one of her brothers instead of her, but she later decided to become an actress anyway. She enrolled at the Lee Strasberg Theatre Institute, and began auditioning for commercials, but soon lost interest: "I didn't want to promote Wonder Bread." She shifted her focus to film and theater, making her first stage appearance in the Off-Broadway play Sophistry with Ethan Hawke, in which she had two lines. Around this time, she began studying at Professional Children's School (PCS), a private educational institution for aspiring child actors in Manhattan. At age nine, Johansson made her film debut as John Ritter's daughter in the fantasy comedy North (1994). She says that when she was on the film set, she knew intuitively what to do. Johansson later played minor roles including as the daughter of Sean Connery and Kate Capshaw's characters in the mystery thriller Just Cause (1995), and an art student in If Lucy Fell (1996).