What makes real life contractual arrangements? How does the law influence real life contractual arrangements? These are everyday questions for businesspeople and commercial lawyers. The traditional ‘imperative’ view of law assumes that business people contract ‘in the shadow of the law’ and contractual arrangements conform to what the law says. But empirical studies on contract practice suggest that contract law may, in fact, play a very insignificant role in real life contractual arrangements. This thesis provides a sociological view of the role of contract law in real life contractual arrangements in the context of the Vietnamese market. Specifically, this thesis applies an institutional law & economics approach to investigate how social structures of the market influence contractual arrangements to marginalize contract law in the Vietnamese market. Drawing on two surveys of contract behaviour in the Vietnamese market, this thesis finds that real life contractual arrangements respond to the institutional structure of the market as a whole, rather than only ‘the shadow of the law’. Institutional changes in the Vietnamese market suggest that there exists a merchant law system, constituted of traditional moral norms and social structures in the market. This merchant law system continues to order contractual arrangements in the market, despite the introduction of a transplanted contract law system. Disagreeing with the imperative approach, this thesis claims that contract law reform should conform to the institutional structure of the market to reduce transaction costs of contracting and to provide an effective framework for real life contractual arrangements.