Contemporary administrations very often act through private entities in the form of a wide range of public-private partnerships (PPP). These partnerships exist in all kinds of administrative activity (intervention, provision and promotion) and take the shape of various legal forms (contracts, concessions, conventions, agreements, subsidies, accreditations, authorisations, etc.). Despite their diversity, all these public-private partnerships present common challenges for the Administration, in at least five areas: choice of a public-private partnership, definition of the partnership, selection of partner, management and control of partners and relations between private partner and citizens. For all these spheres, we can consider a general legal regulation, adaptable or adjustable through sectorial regulations.