This article puts forward the claim that private law, and especially contract and tort, is the area of law that most clearly shows how law depends on social interactions. Taking its cue from Lon Fuller, interactional law is presented as a form of law that depends on informal social practices. Using tort and contract cases, it is argued that this implies that law is in open connection to moral norms and values, and that law cannot be understood without taking into account people’s everyday reciprocal expectancies.

Two phenomena that challenge theories of law in the beginning of the twenty-first century are the regulatory explosion and the emergence of horizontal and interactional forms of law. In this paper, I develop a theory that can address these two phenomena, namely legal interactionism, a theory inspired by the work of Fuller and Selznick. In a pluralist approach, legal interactionism recognizes both interactional law and enacted law, as well as other sources such as contract. We should aim for a pluralistic and gradual concept of law. Because of this pluralist and gradual character, legal interactionism can also do justice to global legal pluralism and to the dynamic intertwinement of health law and bioethics.