Celebrated every year on November 10.
November 10 is the anniversary of the first broadcast of Sesame Street on public television in 1969.
The program of course featured the puppets of Jim Henson.
The aim was in a time where television for children had a reputation of being too violent and commercial, to bring a program that was both fun and educational.
Just like Mister Rogers, but with more puppets and less sweaters.