Hi Dan, Piketty, Elizabeth Warren, etc. who've though about implementing this realize that it does need a worldwide effort or the rich will just migrate. US citizens pay taxes no matter where they live but offshore hiding of money needs to be tackled. A possible solution to renouncing US citizenship is a one-time large tax on such people. Exponential growth has been going on for a long time and probably can't continue in a finite world. Therefore ROI will have to fall. If not, the rich will eventually own everything. Can you think of any alternatives?