How should markets be regulated? In an age of unstable financial markets that have grown ever more complex and where failed regulation can have an enormous detrimental impact, theorizing about this question has largely been dominated by an unfruitful polarization between those who display blanket enthusiasm and those who are downright distrustful of markets. This project aims to rethink the question how to regulate markets and overcome the limitations of existing approaches in economics and philosophy. It provides a political philosophical investigation of what can legitimately be expected of a market regulation theory. Innovations are proposed in each of the three main areas that a regulation theory needs to cover. With respect to normative principles, I will develop the outlines of a capability theory which has as its main focus people?s ability to act as autonomous individuals in markets. To make for an adequate regulation theory, this normative theory will then be confronted with two areas of empirical work. In political economy new work shows that there are several ?varieties of capitalism?, each requiring different forms of regulation. In the experimental social sciences new research largely rejects the standard economic image of self-interested actors (so-called ?homo economicus?) in favor of a more realistic conception of human nature, in which people are much more willing to cooperate with each other. Overall, this breaks new ground in political philosophy, where the prevailing anti-commodification approach has neglected the question of market regulation, in favor of a concentration on markets that should be prohibited or abolished. But some markets are here to stay, and we need to study how to make them function so as to make them function in the wider public interest.