Barbie & Chelsea: The Lost Birthday is a 2021 animated adventure comedy television film directed by Cassandra "Cassi Simonds" Mackay and written by the Ann Austen and Nathaniel "Nate" Federman from a story by Charlotte Fullerton.

The 38th entry in the Barbie film series and the third to feature Barbie's family and/or friends after Barbie Dreamhouse Adventures and Barbie: Princess Adventure, it was first released on 16 April 2021 on Netflix in the United States. The film plot centers on Barbie's in-universe youngest sister, Chelsea Roberts, as she goes on a fantasy-themed adventure on a jungle island to save her 7th birthday she thinks is lost whiles with her family on an adventure cruise ship which by one late night crosses the International Date Line. The film release was accompanied by its soundtrack album, Barbie & Chelsea: The Lost Birthday and More!, which was released on global music streaming services.