A financial transactions tax (FTT) is a tax on wholesale capital market transactions, which civil society has long advocated for on grounds of social justice. This so-called “Robin Hood Tax” would take from the rich and give to the poor. Revenue estimates for a global FTT of 0.05 percent are around US$500 billion per annum. One-quarter of this revenue stream can achieve the first six Millennium Development Goals relating to poverty, health, and education. Even if the developed countries retain all of the revenue raised, the impost would see financial services institutions making a fairer contribution to the societies in which they operate. Thus, as an instrument of justice, the potential of an FTT is great—but, most of all, such a tax will enhance the operations of contemporary financial markets substantially. This paper explores the potential of such a tax, the arguments for and against it, and its feasibility.