Humpday is a 2009 American mumblecore comedy-drama film directed, produced, and written by Lynn Shelton and starring Mark Duplass, Joshua Leonard, and Alycia Delmore. It premiered at the 2009 Sundance Film Festival. International distribution rights were purchased by Magnolia Pictures for a mid-six figure sum. The film opened in New York City in a limited release on July 10, 2009. The story line follows two male heterosexual best friends, Ben and Andrew. The plot line centers around a "mutual dare" that is introduced at a party, which involves the two main characters engaging in a pornographic film together. The film was shot on-location in Washington state around Seattle from September 2008 to January 2009, and much of the dialogue for the film was improvised.

Mumblecore is a subgenre of independent film characterized by naturalistic acting and dialogue, low budgets, an emphasis on dialogue over plot, and a focus on the personal relationships of young adults. Filmmakers associated with the genre include Andrew Bujalski, Lynn Shelton, the Duplass brothers Mark and Jay, Greta Gerwig, Aaron Katz, Joe Swanberg, and Ry Russo-Young. In many cases, though, these directors reject the term. The genre is a mostly American phenomenon. The related term mumblegore has been used for films mixing the mumblecore and horror genres.