UK NHS contracts mediate the relationship between dental and medical practitioners as independent contractors, and the state which reimburses them for their services to patients. There have been successive revisions of dental and medical contracts since the 1990s alongside a change in the levels of professional dominance and accountability. Unintended consequences of the 2006 dental contract have led to plans for further reform. We set out to identify the factors which facilitate and hinder the use of contracts in this area. Previous reviews of theory have been narrative, and based on macro-theory arising from various disciplines such as economics, sociology and political science. This paper presents a systematic review and aggregative synthesis of the theories of contracting for publicly funded health care. A logic map conveys internal pathways linking competition for contracts to opportunism. We identify that whilst practitioners' responses to contract rules is a result of micro-level bargaining clarifying patients' and providers' interests, responses are also influenced by relationships with commissioners and wider personal, professional and political networks.