Some countries treat public-private partnerships (PPP) within public procurement legislation, whilst others adopt a specially designed PPP law to distinguish PPPs from the routine purchases of goods and services. There is no evidence to suggest which of the approaches is more efficient. Differences are visible even for highly developed economies such as the UK (no special PPP law, rather policy guidance) and the US (special PPP laws adopted in over 30 States, counting.) Does it make sense to have a special PPP legislation? If yes, what should such legislation govern? The last question seems tautological as "a PPP legislation should govern public-private partnerships", yet we claim that in order to promote economic efficiency, the law should focus on the environment that surrounds public-private relationships. We develop a model of PPP based on the system of standard contractual agreements between the government and the private sector, like the typical contracts used in public procurement. Due to the asymmetric information, some socially desirable projects are too costly to run within a standard procurement contract, this is where partnerships should help. Specific features that are needed to make those costly projects feasible, include a reduction in the information costs through a closer monitoring within the co-production, a reduction in the production costs through a lesser red tape, and extra benefits (distinct from subsidies and monetary rewards) to the private partner, arising from the cooperation with the state (e.g. reputational gains, access to new resources, etc.) In an institutional/cultural environment with [most of] these features in force, a special PPP legislation is not needed (UK and Australia are prominent examples), as there is no scope for a further reduction of the number of infeasible (costly) projects. Otherwise, a PPP law that offers the above features (e.g. by creating a dedicated PPP advisory unit) is socially desirable.