Until the 2008 financial crisis, tax havens were generally seen as exotic sideshows to the global economy, Caribbean islands or Alpine financial fortresses frequented by celebrities, gangsters, and wealthy aristocrats. Since then, the world has woken up to two sobering facts: first, the phenomenon is far bigger and more central to the global economy than nearly anyone had imagined; and second, the biggest havens aren't where we thought they were. Tax havens collectively cost governments between $500 billion and $600 billion a year in lost corporate tax revenue, depending on the estimate (Crivelli, de Mooij, and Keen 2015; Cobham and Janský 2018), through legal and not-so-legal means. Of that lost revenue, low-income economies account for some $200 billion—a larger hit as a percentage of GDP than advanced economies and more than the $150 billion or so they receive each year in foreign development assistance.