This chapter explains the important role that public law, particularly administrative law, plays in environmental law. This role comes about because much of environmental law requires vesting decision-making and regulatory power in the hands of public decision-makers at all levels of government. This chapter begins by providing an overview of the different constituent elements of public law: constitutional law, administrative law, the role of the EU and international law, as well the complexities of this area of law. The chapter then moves on to consider the way in which the different types of interests involved in environmental problems and the need for information and expertise provide challenges for public law. The chapter then provides an overview of four major features of public law that are particularly relevant to environmental lawyers: the Aarhus Convention, accountability mechanisms, judicial review, and human rights.