The American wealthy are hands down the most philanthropic in the world. Americans dominate global giving lists and surveys consistently show that the U.S. rich are far more likely to make philanthropy a priority.
But some say they could give more. One recent study found that a large share of people making $200,000 or more give only 2.8 percent of their income to charity. Other studies show that multi-millionaires donate only about one percent of their wealth to charity (though billionaires tend to give a higher percentage).
(Read more: Stars of 'Nerd Philanthropy' Dominate Top Giver List)
Warren Buffett and Bill Gates launched their Giving Pledge in large part to persuade the super-rich and the non-super-rich alike to give more to charity. As Buffett told me in 2011, "The hope is that our larger population ends up giving a larger proportion of their income to fund philanthropy."
So why don't the rich give more?