A total of 40 U.S. billionaires have pledged to give away at least 50 percent of their wealth as part of a campaign by investor Warren Buffett and Microsoft founder Bill Gates.

Gates and Buffett launched The Giving Pledge in June to convince hundreds of U.S. billionaires to give away most of their fortune during their lifetimes or after their deaths and to publicly state their intention with a letter of explanation.

Here are some excerpts from letters written by billionaires taking the pledge:

* Laura and John Arnold, hedge fund manager: We view our wealth in this light -- not as an end in itself, but as an instrument to effect positive and transformative change.

* New York City Mayor Michael Bloomberg: If you want to do something for your children and show how much you love them, the single best thing -- by far -- is to support organizations that will create a better world for them and their children. And by giving, we inspire others to give of themselves, whether their money or their time.

* Philanthropist Eli and Edythe Broad: Those who have been blessed with extraordinary wealth have an opportunity, some would say a responsibility -- we consider it a privilege -- to give back to their communities, be they local, national or global.

* Investor Warren Buffett: Were we to use more than one percent of my claim checks (Berkshire Hathaway stock certificates) on ourselves, 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.

* Microsoft founder Bill and Melinda Gates: We have been blessed with good fortune beyond our wildest expectations, and we are profoundly grateful. But just as these gifts are great, so we feel a great responsibility to use them well. That is why we are so pleased to join in making an explicit commitment to the Giving Pledge.

* Hotel magnate Barron Hilton: It is my hope that others are inspired by my father's story, and by our family's steadfast adherence to his charitable philosophy.

* Corporate executive Jon and Karen Huntsman: It has been clear to me since my earliest childhood memories that my reason for being was to help others.

* Banker George Kaiser: I had the advantage of both genetics (winning the 'ovarian lottery') and upbringing. As I looked around at those who did not have these advantages, it became clear to me that I had a moral obligation to direct my resources to help right that balance.

* Media entrepreneur Gerry and Marguerite Lenfest: The ultimate achievement in life is how you feel about yourself. And giving your wealth away to have an impact for good does help with that feeling.

* Business Wire founder Lorry Lokey: There's an old saying about farmers putting back in to the ground via fertilizer what they take out. So it is with money. The larger the estate, the more important it is to revitalize the soil.

* Moviemaker George Lucas: My pledge is to the process; as long as I have the resources at my disposal, I will seek to raise the bar for future generations of students of all ages. I am dedicating the majority of my wealth to improving education.

* Tashia and John Morgridge, former Cisco CEO: The more personally involved we have become with the causes we support the more effective we seem to be.

* Peter Peterson, founder of Blackstone Group equity firm: As I watched and learned from my father's example, I noticed how much pleasure his giving to others gave him. Indeed, today, I get much more pleasure giving money to what I consider worthwhile causes than making the money in the first place.

* David Rockefeller, patriarch of the Rockefeller family: Our family continues to be united in the belief that those who have benefited the most from our nation's economic system have a special responsibility to give back to our society in meaningful ways.

* Jeff Skoll, former eBay executive: The world is a vast and complicated place and it needs each of us doing all we can to ensure a brighter tomorrow for future generations.

* Asset manager Tom Steyer and Kat Taylor: Surely the pleasure we derive from St. Francis' active verbs of consoling, understanding, loving, giving and pardoning far outweigh any selfish and passive pleasures of owning, having, or possessing.

* Media magnate Ted Turner: I'm particularly thankful for my father's advice to set goals so high that they can't possibly be achieved during a lifetime and to give help where help is needed most. That inspiration keeps me energized and eager to keep working hard every day on giving back and making the world a better place for generations to come.

* Former Citigroup executive Sanford and Joan Weill: Our Pledge is this: We will continue to give away all of the wealth we have been so fortunate to make except for a very small percentage allocated to our children and grandchildren between now and the time we pass because we are firm believers that shrouds don't have pockets.

Source: www.givingpledge.org

George Lucas Ted Turner Michael bloomberg Warren buffett