A Teacher is a 2013 American drama film written and directed by Hannah Fidell, in her feature directorial debut. It revolves around a female high school teacher's illicit sexual relationship with a male student that turns from infatuation into obsession. Principal photography for the film took place in Austin, Texas. The film had its premiere at the 2013 Sundance Film Festival on January 20, 2013. The film was released on video on demand on August 20, 2013, prior to receiving a limited release on September 6, 2013, in the United States.

While praise was given towards the film's performances, cinematography, score, and its attempt to explore a complex issue, criticisms were reserved over a narrative lack of focus, exposition, and character development. In 2014, it was announced the film would be adapted as a TV series, with Fidell executive producing. Kate Mara became attached to star as the lead and also as an executive producer. A Teacher, the resulting miniseries, premiered on FX on Hulu in November 2020.