Governments are increasingly turning to the private sector to provide the capital, resources and/or know-how necessary for development and operation of infrastructure. In some cases, the involvement by the private sector will trigger coverage by an international investment treaty that overlies, and can override, the domestic law and contract that would otherwise be applicable to the project. This paper discusses the circumstances affecting when an investment treaty will apply and also highlights some of the ways that investment treaties can impact governance of infrastructure development and operation. While focusing on the relationship between investment treaties and investments in infrastructure, this paper is also relevant for the connections between investment treaties and other activities involving investor-state contracts (or quasi-contractual relationships) such as investments in the extractive industries.