Global income and wealth inequality have increased dramatically in the last decade. Public money for acutely needed action on social and environmental problems is missing. The excessive wealth concentration erodes our societies’ social contracts and challenges the independence of democratic institutions. Calls for progressive taxation are getting louder to make the rich pay their fair share. But even in states with a progressive income tax, billionaires may pay very little taxes because they channel their assets in ways that reduces their taxable income. How could this be avoided? Would a progressive wealth tax solve the problem? How would it lead to a redistribution of wealth to middle class and lower income groups? How could it help to fund a social-ecological transformation? What measures against tax evasion and tax avoidance are necessary to ensure that rich individuals or Multinational Corporations do not hide their money in assets that are subject to tax exemptions, tax havens or in foreign financial institutions? How does the ongoing reform process of the international tax system reflect on these questions?