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.
On the whole, Americans have given more than $300 billion per year in recent years, though giving has declined since the start of the recession, according to the Giving USA Foundation.
"We're hoping that America, which is already the most generous society on Earth, becomes even more generous over time," Buffett told reporters on a conference call today. "More philanthropy and smarter philanthropy in the future is the goal."
Besides inspiring others to give, the pledged sums promise to make a huge impact.
"Private dollars are really special dollars because they provide the ability to innovate, to take risks, to think outside the box," said Gordon Campbell, president and CEO of United Way of New York. "Just think of the possibilities."
"I think it's a stopgap at a time when charities are facing a dip in income," said Jennifer Tierney, development director for Doctors Without Borders in the U.S. "It's a great way to fill the time between the recession and when the country gets back on its feet and your everyday American citizen is able to support in the same way that they have been able to in the past."
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.
Giving Pledge participants will meet to share advice on the best ways to put their large fortunes to good use.
"The idea is not to tell anybody when or how to do it, but at least offer what others have learned," Buffett said. "We've found that when we do this at dinners, everybody goes away smarter at the end of it."
Buffett and Bill and Melinda Gates reached out to some 80 members of the Forbes billionaires list, asking them to sign on. Over the last month and a half, they personally called and hosted private dinners, hoping to convince them to pledge. About half agreed, and they'll continue to push for others to join in the cause. Right now, the Giving Pledge is focused on Americans, but the campaign could eventually expand worldwide.
"They're really strong-arming them to do this, and they're doing it themselves," said Matthew Miller of Wealth-X, which tracks the world's richest people.
Miller added that that not everybody says yes, and there's even something of a backlash among the super-rich.
"Some billionaires are saying, 'You know, I don't really need to be called out publicly,'" said Miller. "[They say] 'I don't appreciate it. It's a publicity stunt.'"
Still, plenty have signed on to a list that includes "old money" families and the self-made. The names include corporate titans, entertainers, oil executives and politicians. In their personal letters, each shared some of their individual philosophies on giving.
"By giving, we inspire others to give of themselves, whether their money or their time," wrote New York City Mayor Michael Bloomberg.
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."
Former Citigroup executive Sandford Weill and his wife Joan described their motivation for participating, writing that "we are firm believers that shrouds don't have pockets."
"I'm not a big fan of inherited wealth. It generally does more harm than good," wrote oil tycoon T. Boone Pickens, adding that while he enjoys making money, giving it away is a "close second."
In an exclusive statement to ABC News, signatory Pete Peterson wrote, "As millions of Americans suffer the hardships of a deep recession, as the economy's future gets ever more uncertain, and as the public's concern about Washington's political obstructionism gets ever more intense, I think private philanthropy has a unique and urgent role to play in both helping the less fortunate and in educating, motivating, and activating the American public to get this nation on a sounder course."
In another exclusive statement, David Rubenstein, co-founder and managing director of the Carlyle Group, said, "I regard it as a repayment of a debt to the country that has been so generous to my family and me. I hope that the attention the pledge receives will encourage all Americans--not just a select few--to consider increasing their own giving to worthy organizations and causes. If that occurs, the pledge will have really achieved its most important aim."
1. Bill and Melinda Gates
2. Warren Buffett
3. Larry Ellison
4. Michael R. Bloomberg
5. Paul G. Allen
6. Ronald O. Perelman
7. George B. Kaiser
8. Jim and Marilyn Simons
9. Eli and Edythe Broad
10. Pierre and Pam Omidyar
11. Michele Chan and Patrick Soon-Shiong
12. Laura and John Arnold
13. George Lucas
14. Barron Hilton
15. David M. Rubenstein
16. Jeff Skoll
17. David Rockefeller
18. Julian H. Robertson, Jr.
19. Peter G. Peterson
20. Walter Scott, Jr.
21. Ted Turner
22. Ann and John Doerr
23. Tashia and John Morgridge
24. Bernie and Billi Marcus
25. Alfred E. Mann
26. Herb and Marion Sandler
27. Joan and Irwin Jacobs
28. Tom Steyer and Kat Taylor
29. Barry Diller and Diane Von Furstenberg
30. T. Boone Pickens
31. Bernard and Barbro Osher
32. Elaine and Ken Langone
33. Jon and Karen Huntsman
34. Thomas S. Monaghan
35. Gerry and Marguerite Lenfest
36. Jim and Virginia Stowers
37. Vicki and Roger Sant
38. Shelby White
39. Lorry I. Lokey
40. Sanford and Joan Weill
ABC's Dan Arnall, Bianna Golodryga, Eric Noll, and Christina Brozyna contributed to this report.