Seventeen more of the wealthiest families and individuals in the United States have joined Microsoft co-founder Bill Gates and billionaire investor Warren Buffett in a pledge to give at least half their wealth to charities over their lifetime and beyond.

About four months after launching a plan to convince the wealthiest Americans to donate large portions of their accumulated wealth, The Giving Pledge has logged 57 signatories. Gates and Buffett estimated in August their efforts could generate $600 billion dollars in charitable giving.

"We're off to a terrific start," Buffett said.

Among those making up the latest round of pledges released on Wednesday is Facebook co-founder and CEO Mark Zuckerberg. “People wait until late in their career to give back. But why wait when there is so much to be done?” said Zuckerberg.

“With a generation of younger folks who have thrived on the success of their companies, there is a big opportunity for many of us to give back earlier in our lifetime and see the impact of our philanthropic efforts,” Zuckerberg said.

The pledge is a moral commitment to give, not a legal contract, nor does it involve pooling money or supporting a particular set of causes or organizations. However, several of those who have made the pledge have already displayed their preferences for supporting environmental and clean energy causes.

Other well known names that have signed on to the pledge include New York City Mayor Michael Bloomberg, movie producer George Lucas, media magnate Ted Turner, Microsoft co-founder Paul Allen, and Texas oilman-turned-wind-energy-advocate T. Boone Pickens.

Much like the structure of the Clinton Global Initiative, those who take the pledge will come together at an annual event to share ideas, learn from (and keep tabs) on each other.