Towards a Socio-Legal Theory of Contractual Risk - This paper deals with the risk of opportunism the usual risk in economic exchanges. Breach of contract is probably the most common event in daily life and has therefore attracted research and debates in many disciplines of the social sciences. This discussion deals with the current knowledge of the ways in which societies are coping with the risk of opportunism, distinguishing between three approaches with ascending degrees of complexity: theories of institutional support of contractual exchanges, theories of relational trust and theories of social systems of trust. As demonstrated in Fig. 1 these theories are chosen among many other competing approaches. Rather than being replaced by institutional economics or economic sociology, socio-legal knowledge is a necessary and valuable ingredient for theories of contractual risk. Without our knowledge of the protection of property rights in a particular society, of choices between formal and informal modes of conflict resolution made by business people or consumers, of obstacles in court proceedings and of problems when a lawyer is consulted, our neighbour disciplines come to either over-optimistic conclusions as regards institutional trust or to oversimplified models as regards personal trust and relationships.