In the context of a reconfigured public-private regulatory landscape, this thesis analyses, through the lenses of administrative law, regulatory activities with a public law impact. It critically assesses whether those activities are performed by non-state regulators in compliance with administrative law principles that are required for this kind of activity when performed by a public regulator. It proposes a tailored use of administrative law principles as public law control for such regulatory activities. Three separate levels of engagement with regulation are pin-pointed. First, the movement from private actors internalizing a public logic in regulation to private actors performing as regulation shapers; second, the progression from administrative law principles applied to public regulation to administrative law-like principles applied in non-conventional forms of regulation; third, the evolution from a preeminently subject-centered logic in administrative law to an increase in the use of a functional logic. These underlying trajectories will be demonstrated through three different examples of non-conventional forms of regulation: regulation through information, regulation through standards and regulation through professional codes. The presence of administrative law principles in these examples of non-conventional forms of regulation will be analysed with a focus on whether and how they contribute to governing the relationship between these non-conventional regulators and citizens. This work is structured as follows. Chapters two and three analyse administrative laws adaptative capacity, in domestic and beyond the state settings, respectively, providing the theoretical framework for administrative law. Chapter two will show how administrative law has developed in different national contexts to adapt to new phenomena over time. The adaptative capacity of administrative law will become more evident in chapter three in relation to new phenomena beyond the state, where nonstate actors are emerging as more relevant in regulatory and governance areas. Chapter four provides a theoretical framework for regulation and analyses it in relation to administrative law as portrayed in previous chapters. This chapter attempts to understand what is meant by regulation in the context presented in previous chapters. Chapter five presents three examples that illustrate the interplay between private and public rule-makers at different levels as well as the concerns that may arise from a public law point of view.