Cari Tuna, wife of Facebook co-founder Dustin Moskovitz.

SAN FRANCISCO, CA- NOVEMBER 23: Cari Tuna photographed in her office in San Francisco, California on November 23, 2014. Cari Tuna, 29, is the wife of Facebook co-founder Dustin Moskovitz. They are the youngest couple to sign on to The Giving Pledge -- the campaign to get billionaires to give away more than half their wealth to charity. They are worth about $6.8 billion. Cari leads the couple's charitable foundation and is going about trying to figure out how to give that money away to maximize its impact. She's taking a very scientific approach and has tons of spreadsheets and has interviewed more than 300 people ranging from Bill Gates to Brookings scholars and doctors in Burma. They are planning to announce their first big gifts in January or February so we thought we'd get out ahead of the announcement with a profile in late December. Her foundation has already donated a lot of money to global health/development as she is very interested in what can be done about poverty. However, the interesting thing about her approach is that she's trying to follow logic rather than her passions. It's a completely different philosophy of giving than many of her Silicon Valley contemporaries. (Photo by Marvin Joseph/The Washington Post via Getty Images)