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Warren Buffett (right) speaks to the media with Bill and Melinda Gates on June 26, 2006 at a news conference where Buffett spoke about his financial gift to the Bill and Melinda Gates Foundation in New York City.
Bill Gates has held the title of richest person in the world many times since 1995, recently falling to second place behind Amazon CEO Jeff Bezos. Over the past two decades, Gates and his wife, Melinda, have spent much of their money on charity, encouraging other billionaires to follow in their footsteps by signing the Giving Pledge.
The Gates couple launched the pledge with Warren Buffett in 2010, asking signatories to donate a majority of their wealth to charity either during their lifetime or in their will.
In the Bill and Melinda Gates Foundation's annual letter from this year, Gates wrote that he and his wife discussed spending a lot of time on philanthropy before they even got married.
"We think that's a basic responsibility of anyone with a lot of money," Gates wrote. "Once you've taken care of yourself and your children, the best use of extra wealth is to give it back to society."
This is how Gates and other billionaires in the tech industry spend the money they pledged to donate: