Thumbsucker is a 2005 American independent comedy-drama film written and directed by Mike Mills in his feature directorial debut. The film stars Lou Taylor Pucci, Tilda Swinton, Vincent D'Onofrio, Kelli Garner, Benjamin Bratt, Vince Vaughn, and Keanu Reeves. The plot focuses on Justin Cobb, a teenager in suburban Oregon, as he copes with his thumb-sucking problem, romance, and his diagnosis with ADHD and subsequent experience using Ritalin. The screenplay was adapted from the 1999 Walter Kirn novel of the same name. Swinton also served as an executive producer.

The film was shot on location in the Portland metropolitan area in 2003, and premiered at the Sundance Film Festival in January 2005. It received a limited release in the United States on September 16, 2005.