These 23 Americans are changing the world - and they're all under 40

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The World Economic Forum recently announced its 2016 class of Young Global Leaders - people under the age of 40 who are changing the world - and 23 of the 121 are American.

This year's Young Global Leaders class includes leaders from an array of backgrounds. Some are famous entertainers, like actor and investor Ashton Kutcher and writer John Green, and others are inventors, CEOs, philanthropists, and scientists working on revolutionary ideas - such as Nina Tandon, who grows human bones with her biotech company, EpiBone.

Once chosen by the WEF, these leaders are a part of the program for five years - they attend meetings, participate in initiatives and research, and work with the rest of the WEF's community.

Here are the 23 American leaders making a worldwide impact.