Directed by Henry Coster
Written by Mary Chase and Oscar Bodney
Trailer
IMDB

Jimmy Stewart plays a man who has a spirit animal, which is a 6'8" rabbit named Harvey. Stewart's sister decides that she is going to commit him because it's hard for her to throw a party. There's a mix-up and she ends up getting committed when she admits to seeing Harvey sometimes.
This is a great film, funny and somewhat heart-warming without ever getting heavy handed or overly dramatic. Stewart is one of the greatest actors ever, if not the best. This movie is a showcase for his superb acting talent. Josephine Hull, who won an Oscar for her role, is also excellent as Stewart's crackpot sister.

10/10