One of the great reasons to visit Yellowstone National Park is to see the animals.
Yellowstone abounds with some of North America's most iconic animals: bison (commonly mis-named as buffalo), elk, bears, deer, and many others.
The are huge numbers of bison all over the park; they are by far the most visible animals. There are herds of tens, or even hundreds of them along river flats, and individuals just pop up everywhere as you travel around.