We are well aware of the rise of the 1% as the rapid growth of economic inequality has put the majority of the world's wealth in the pockets of fewer and fewer. One much-discussed solution to this imbalance is to significantly increase the rate at which we tax the wealthy. But with an enormous amount of the world's wealth hidden in tax havens--in countries like Switzerland, Luxembourg, and the Cayman Islands--this wealth cannot be fully accounted for and taxed fairly. No one, from economists to bankers to politicians, has been able to quantify exactly how much of the world's assets are...