(Flashback) As a child, Amelie lived a very sheltered life, didn't go to school, and had no friends. When she was six, her mother suddenly died, leaving her with her indifferent father.
(The present) Now she is 23, and having left home, she is working in a cafe in Paris. On the day Princess Diana is killed in a car crash, she discovers a box hidden in her flat, containing some treasured objects that a young boy hid away in the 1950's. She decides to find him, and give it back to him.
She succeeds, making this man happy, and now sets out to make everybody she can happy, in subtle and amusing ways. (One example: her neighbour tells her a story about her late husband. Amelie reads some letters from this man, "invents" a new letter by piecing together some of the old ones, and sends it to the neighbour, with a note saying it was lost for 30 years.)
But she doesn't do so well in making herself happy. Nino, a young man who Amelie fancies, collects discarded photos from photo booths, and sticks them in an album, which he loses. Amelie finds it, and devises complicated ways of returning it to him. Although she loves him, can Amelie bring herself to meet him?
In the photo album, there is also a mysterious man who keeps reappearing: taking his picture in photo booths all over Paris, only to throw them away. Is he someone afraid of growing old, or a dead man who is afraid of being forgotten?