A new book, "Like: The Button That Changed The World," delves into the convoluted story behind the symbol.

YouTube and another early video site, Vimeo. Facebook unquestionably turned the Like button into a universally understood symbol, while profiting the most from its entrance into the mainstream.

Facebook unquestionably turned the Like button into a universally understood symbol, while profiting the most from its entrance into the mainstream. FriendFeed, a rival social network created by ...