"Lisa's Date with Density" is the seventh episode of the eighth season of the American animated television series The Simpsons. It originally aired on the Fox network in the United States on December 15, 1996. It was written by Mike Scully and directed by Susie Dietter. The writers wanted a "silly" Homer story to balance the episode out, By this time, the show had begun to have episodes revolving around secondary characters. This was the first episode to revolve around Nelson, and was done to partly explain why Nelson acts the way he does. There was a debate as to how injured Milhouse should look without it looking disturbing, and the drop of blood coming from his nose was decided to be enough.
The authors of the book I Can't Believe It's a Bigger and Better Updated Unofficial Simpsons Guide, Gary Russell and Gareth Roberts, called it "impressive" how "even after Nelson has beaten [Milhouse] up for apparently making a pass, [Milhouse] will still do anything for uncaring Lisa."
Yeardley Smith, the voice actress of Lisa, has mentioned this episode is one of her favorite Simpsons episodes of all time.
This is also one of several episodes that has been performed live by the cast in front of an audience.