Big is a 1988 American fantasy comedy film directed by Penny Marshall and stars Tom Hanks as Josh Baskin, an adolescent boy whose wish to be "big" transforms him physically into an adult. The film also stars Elizabeth Perkins, David Moscow, John Heard, and Robert Loggia, and was written by Gary Ross and Anne Spielberg. It was produced by Gracie Films and distributed by 20th Century Fox.

Upon release, Big was met with wide critical acclaim, particularly for Hanks' performance. It was a huge commercial success as well, grossing $151 million worldwide against a production budget of $18 million, and it proved to be pivotal to Hanks' career, establishing him as a major box-office draw as well as a critical favorite. The film received Academy Award nominations for Best Actor (Hanks) and Best Original Screenplay.

Thirteen-year-old Josh Baskin tries to impress a girl by going on a carnival ride but is refused as he is too short. Dejected, he inserts a coin into an antique fortune-teller machine called Zoltar, and makes a wish to be "big". It dispenses a card stating "Your wish is granted," but Josh discovers the machine has been unplugged the entire time.

The next morning, Josh discovers that he has grown physically into an adult. Thinking that this proves that the Zoltar machine can actually make wishes come true, he tries to locate the machine, but finds that the carnival has moved on. Returning home, he desperately tries to explain his predicament to his mother, who panics and chases him from the house thinking he is a stranger who has kidnapped her son. He then finds his best friend Billy at his school and convinces him of his identity by reciting a song that only they know. With Billy's help, Josh learns that it will take at least six weeks to find the Zoltar machine again, so Josh rents a room in a flophouse in New York City and gets a job as a data entry clerk at the MacMillan Toy Company.

Josh meets the company's owner, Mr. MacMillan, at FAO Schwarz, and impresses him with his insight into current toys and his child-like enthusiasm. They use the store's Walking Piano to play duets ("Heart and Soul" and "Chopsticks"), and MacMillan invites Josh to a massive marketing campaign pitch meeting with senior executives. Unimpressed with the toy being pitched, Josh shocks and challenges the executives with a simple declaration that the toy is not fun, and while his follow-up suggestions invigorate the team for new ideas, he earns the animosity of Paul Davenport, the pitch's leader. Meanwhile, a pleased MacMillan promotes Josh to Vice President of Product Development. He soon attracts the attention of Susan Lawrence, a fellow executive, and a romance begins to develop, much to the dismay of her former boyfriend Davenport. Josh becomes increasingly entwined in his adult life by spending time with Susan, mingling with her friends, and entering into a steady relationship with her. His ideas become valuable assets to MacMillan Toys; however, he begins to forget what it is like to be a child, and his tight schedule rarely allows him to spend time with Billy.

MacMillan asks Josh to come up with proposals for a new line of toys. He is intimidated by the need to formulate the business aspects of the proposal, but Susan says that she will handle the business end while he comes up with the ideas. Nevertheless, he feels pressured and longs for his old life. When he expresses doubts to Susan and attempts to explain that he is a child, she interprets this as fear of commitment on his part and dismisses his explanation.

Josh learns from Billy that the Zoltar machine is now at Sea Point Park, and he leaves in the middle of his presentation to MacMillan and the other executives. Susan follows Billy, who tells her where Josh went. At the park, Josh finds the machine, unplugs it, and makes a wish to become a child again. He is then confronted by Susan for running off, but upon seeing the machine and the fortune, she realizes that he was telling the truth and becomes despondent that their relationship will end. Josh thanks her for their time together and suggests she use the machine to turn herself into a little girl. Susan declines, but offers to drive Josh back to New Jersey. After sharing an emotional goodbye with Susan, Josh transforms into a child again before reuniting with his family and Billy.

The Italian film Da grande (1987) has been said to be the inspiration for Big. Gary Ross and Anne Spielberg developed the story in one hour; days after the script was completed they sold it to James L. Brooks and 20th Century Fox.