Yeardley Smith (IPA: /ˈjɑrdli/; born July 3, 1964) is an Emmy Award-winning American actress and voice actor who is perhaps best known for providing the voice of Lisa Simpson on the animated television series The Simpsons.

Smith was born Martha Maria Yeardley Smith in Paris, France, and was raised in Washington, D.C., U.S. She is the daughter of Martha Mayor, a gallery worker, and Joseph Yeardley "J.Y." Smith (May 10, 1931–January 17, 2006), The Washington Post's first official obituary editor (1977–1988), who continued working full time for The Post until 1996.

In addition to performing as the voice of Lisa Simpson on The Simpsons, Smith appeared on the sitcoms Herman's Head and Dharma and Greg and guest-starred on Showtime's Dead Like Me and the Disney Channel's Phil of the Future. Her résumé features guest appearances on Teen Angel, and the "Mathnet" segment of the Children's Television Workshop show Square One. She also appeared as an escaped juvenile prisoner named "Bonita Rokeke" in an episode of Mama's Family.

Her film credits include The Legend of Billie Jean, City Slickers, Maximum Overdrive and As Good as It Gets. A twist of trivia regarding her work on The Simpsons was that she auditioned for the role of Bart Simpson, while Nancy Cartwright auditioned for the part of Lisa. However the producers felt that Smith would be better suited for Lisa's voice, while Cartwright was given the role of Bart.

Smith won an Emmy for Outstanding Voice-Over Performance for her work on The Simpsons in 1992. Lisa's distinctive voice differs from Smith's only in that it is higher in pitch. Smith has joked about her lack of vocal range in comparison to her Simpsons co-stars, saying she only has three voices: her own, Lisa's, and one that's somewhere in between. She has also said that any time Lisa sings on the show that she has to drop into her own singing voice. Her laugh too however, as heard on the DVD commentaries, also is quite close to Lisa's.

Smith married English-Canadian actor Christopher Grove in 1990 and divorced him in 1992. She is now married to Daniel Erickson; the couple were wed in 2002.

Smith admitted on The Jane Pauley Show that she had struggled with bulimia for 25 years. Her character Lisa Simpson suffered through an eating disorder in the episode "Sleeping with the Enemy". She is currently performing in a one-woman show called More where she exposes her eating disorder. Smith has been binge-purge free since February 18, 2003.