The Most 20 Powerful US CEOs 40 and Under

"Some of them started their own businesses, while others joined established ones and quickly ascended. There are also lucky execs who knew all the right people, and some who took over family businesses. Regardless of how they got there, these young chief executives are the heads of the country’s biggest publicly traded companies by market capitalization, as of Feb. 13, that have CEOs 40 and under."