"Moaning Lisa" is the sixth episode of the American animated television series The Simpsons. It originally aired on Fox in the United States on February 11, 1990. The episode was written by Al Jean and Mike Reiss, and was directed by Wes Archer. Ron Taylor guest stars in the episode as Oscar "Bleeding Gums" Murphy. The episode deals with Lisa's depression and her attempts to sublimate it by playing her saxophone.

Lisa wakes up one morning in a deep depression. At school, she gets in trouble with her music teacher for improvising and becomes reluctant to play dodgeball in gym. At home, Homer and Bart pummel each other at video boxing, but despite Homer's attempts, he is unable to defeat Bart.

Homer and Marge try to cheer Lisa up, but she is consumed with existentialism and worry over all the suffering in the world. In her room, Lisa hears music coming from outside her window. She follows the music through town and meets Oscar "Bleeding Gums" Murphy, a soulful saxophonist playing the blues. Lisa learns about expressing herself through her music from him, only to be discovered and whisked away by Marge.

Homer goes to the arcade and enlists the help of an arcade boxing expert, while Marge, who is still upset at Lisa for sneaking out the night before, takes her to band practice. She tells Lisa to smile no matter how she feels inside, to suppress her emotions to be popular, and that happiness will follow.

But when she sees Lisa hiding her true feelings and being taken advantage of by her classmates and her music teacher, Marge changes her tune and tells Lisa to be herself. Her support helps Lisa to feel genuinely happy. When Homer returns home, he is about to defeat Bart in a rematch but Marge unplugs the game console to announce Lisa's recovery, while Bart declares his retirement as an undefeated video boxing champ. Later, the Simpsons visit a jazz club to hear Bleeding Gums Murphy sing a blues number written by Lisa.

"Moaning Lisa" was the first episode of the series to focus on the character of Lisa Simpson. The idea for it was suggested by The Simpsons producer James L. Brooks, who wanted to do an episode where Lisa was sad but she did not know why. The writers also felt they had done several "jokey" episodes on the show and wanted to try something new that was "really emotional and sweet".

While writers Al Jean and Mike Reiss were initially thrilled to write an episode pitched by Brooks, for whom they had deep admiration, they were unsure that the depression-themed episode would work. Series creator Matt Groening taunted the pair for having been assigned the episode, while producer Sam Simon told them that Brooks had been trying to get such an episode made since Taxi. According to Reiss, the episode establishes Lisa as a character, as in his and Jean's previous episode "There's No Disgrace Like Home", she is as badly behaved as Bart.

The song Lisa sings in this episode later reappeared in expanded form on The Simpsons Sing the Blues CD. Mr. Largo, Lisa's music teacher, was partly inspired by a music teacher Groening had as a child. The designs of the boxers in the video game Homer and Bart play were loosely based on Homer and Bart, and the referee in the game was based on a character from Matt Groening's Life in Hell comic strip. "Bleeding Gums" Murphy was loosely based on the famous blues musician Blind Lemon Jefferson. Ralph Wiggum, "Bleeding Gums" Murphy, and Jacqueline Bouvier (during Marge's childhood flashback) all make their first (going by production order rather than airdate) appearances on The Simpsons in this episode.