Pawn turns into a queen.

I've always wondered why anyone would want anything other than a queen givin the option of bishop, rook, or knight. I can see chosing a knight if that would turn into checkmate upon becoming one, but outside of that why choose anything but a queen? I'm sure that I'm missing something here. What is it?

I think there are a few instances where underpromotion is the way to go. The one you mention with a knight is one. Also, promoting to a queen may create a stalemate.

yes, stalemate. sometime (like i do) you can play with your opponent, like what happened to me in a game against a GM... 4 underpromotions! i couldnt take it..... ummm..... thats all i can think of right now...