The Giving Pledge encourages the world's richest to give away most of their wealth to charitable causes. The campaign was created by Bill Gates and Warren Buffett in 2009 in New York City and made public in 2010. It focuses specifically on billionaires. As stated on its website, 'The Giving Pledge is a commitment by the world's wealthiest individuals and families to dedicate the majority of their wealth to philanthropy.' Pledgers are required to announce their commitment publicly and to write a letter of declaration. As of August 2015, there were more than 130 pledgers committed to the cause. Along with Buffett and Gates, pledgers include Mark Zuckerberg, Michael Bloomberg, David Rockefeller and Sara Blakely -- the first female pledger. The Giving Pledge has expanded to 5 continents. The most popular causes include public health, disease research, education reform, environmental efforts and child welfare. The average pledger's net worth is about $5.7 billion.