This week, Warren Buffett and Bill and Melinda Gates managed to get another 38 billionaires on board their project, The Giving Pledge, in which the mega-rich pledge to give at least half of their money to charities either during or after their death.

That adds up to at least $160 billion, though that amount will probably be exceeded since many of the billionaires have said they will give away almost all of their wealth after they die.

We're featuring 20 of the 40 billionaire givers. Check out the full list here.