This year, Bill and Melinda Gates are doing something a little different with their annual letter. They are answering what they call some of the "toughest questions" from their foundation's critics.
On the list: Is it fair that you have the influence you do? Why don't you give more to the United States? Why do you give your money away?
Since its inception, the Gates Foundation has given $41.3 billion in grants, including a grant to NPR.