WATCH: Biden says Trump wrote a very ‘generous’ transition letter

"The president wrote a very generous letter," said Biden referring to Trump. "Because it was private, I won't talk about it until I talk to him. But it was generous."

The transition letter is customarily written from each outgoing president to their successor congratulating them on their victory and wishing them and their administration luck. Usually the letter is left for the successor on or in the Resolute Desk of the Oval Office. The letters are normally kept private until published at a later date.