At the urging of Bill Gates and Warren Buffett, forty of the world's richest families have promised to give at least half of their fortunes to philanthropy. By taking the Giving Pledge," the forty families or individuals, most of whom are billionaires, are promising a collective sum of at least $125 billion to charitable causes, based on Forbes' current estimates of their net worth and other data sources. According to the pledge, the giving can occur either during donors' lifetimes or after their passing. Each has committed at least 50 percent of their net worth, but many have committed to larger percentages, Buffett said. The men and women taking the pledge are free to direct their money to causes of their choice, and the organization is not pooling any money or dictating areas of need. In fact, the pledge is non-binding, though the organizers say the billionaires are making a "moral commitment," publicly signing their names to letters posted on a website, GivingPledge.org. Buffett and Bill and Melinda Gates reached out to some 80 members of the Forbes billionaires list, asking them to sign on. Buffett wrote that by spending any more than one percent of his fortune on his own family, "neither our happiness nor our well-being would be enhanced. In contrast, that remaining 99 percent can have a huge effect on the health and welfare of others."