How Do You Know is a 2010 American romantic comedy film directed, written and produced by James L. Brooks, and starring Reese Witherspoon, Owen Wilson, Paul Rudd and Jack Nicholson in his final film role. It was the third film to feature Witherspoon and Rudd following Overnight Delivery and Monsters vs. Aliens. The plot follows softball player Lisa (Witherspoon), who is caught in a love triangle between two men—the charming baseball player Matty (Wilson) and George (Rudd), a businessman who is the target of a SEC stock fraud civil suit.

The film was shot in Philadelphia and Washington, D.C., and was released on December 17, 2010. It underperformed at the box office, grossing $48.7 million against a $120 million budget, and received mixed-to-negative reviews from critics.