The Yip Yips (also known as the Martians or Aliens) are characters on the American educational children's television show Sesame Street. They are puppets depicting alien visitors from Mars. with notable physical features such as squid-like tentacles, large eyes, and antennae. Built by Caroly Wilcox, they are "Yip Yipped" by multiple Muppeteers including Jim Henson, Jerry Nelson, Richard Hunt, Martin P. Robinson, and Kevin Clash. The puppets have a very simple design, controlled entirely by two rods (one for the body and eyes, the other for the front of the mouth). This allows their entire bodies to be seen on camera, appearing to float in the air.

The Yip Yips appear by materialising into a room, always saying "Yip-yip-yip-yip... Uh-huh" upon arrival. As they come across common objects they are foreign to them, the Yip Yips consult a book they call "Earth book". When they fail to 'correctly' interact with an object of Earth even after consulting their book, they are known to say "nope nope nope". Another common trait of the Yip Yips is that when frightened, they cover their face with the lower part of their jaw while making a "goom" noise.