Ernie is well known for his fondness for baths with his rubber duckie, and for trying to learn to play the saxophone although he wouldn't "put down the duckie." Ernie is also known for keeping Bert awake at night, for reasons such as wanting to play the drums, wanting to count something (like sheep), to observe something like a blackout, or even because he is waiting for his upstairs neighbor to drop his shoes.
He has a distinctive, chuckling laugh (a trait he shares with his baby cousin Ernestine).
Many Ernie and Bert sketches involve Ernie wanting to play a game with Bert, who would much rather do something else (like read). Ernie keeps annoying Bert with the game until Bert joins in -- and usually, by the time Bert starts enjoying the game, Ernie is tired of playing the game and wants to do something else. Other sketches have involved them sharing some food by dividing it equally, only for one of them to have a bit more than the other, leading Ernie to make it even by eating the extra piece.
Ernie has also frequently made appearances without Bert. He has regularly appeared in skits with Cookie Monster, Sherlock Hemlock and Lefty the Salesman.
From season 33 until season 36, he and Big Bird starred in a daily segment called "Journey to Ernie". Starting in season 39, Ernie and Bert have appeared in animated form in the Bert and Ernie's Great Adventuressegments.