Using analogies from research in simulation and artificial societies and borrowing from Weinrib's Philosophy of Private Law, we show how a “private law” model of law and legal integration does not need to presuppose the state as a regulatory framework. Rather, the state emerges as a “second order property” from the private law interaction of individuals. We apply this to the debate about harmonisation in Europe. We show how a form of unity in diversity can be built up starting with such individual interactions, extended later to interactions between member states. But this does not need to end up in an individualistic and neo-liberal model, as in Weinrib, if we understand the underlying exchange relation in terms of Wilhelmsson's social contract law.