This book focuses on legal frameworks within which regional authorities in EU Member States must act in the course of the necessary transition towards a sustainable energy system. Regional authorities or regional governments are broadly understood here as sub-national bodies that either hold a regional or local authority electoral mandate, or are politically accountable to an elected assembly. The book explores the role played by these regional authorities in this vital transition to renewable energy, and, more specifically, it maps several legal questions that might emerge along the path to renewable energy. Neither the possibilities for the financial promotion of renewable energy, nor the planning and permitting of renewable energy projects and the management of the grid can be understood outside the context of international, EU and national law. This multi-level legal framework has become increasingly complex with renewable energy laws at EU and national levels particularly, having faced frequent amendments complicating an understanding of the applicable law. Alongside specific renewable energy laws, a vast number of other laws are important elements for the transition to renewable energy, since for instance, nature conservation and air quality legislation must be taken into account when deciding on renewable energy activities, such as hydro-power generation and biomass combustion. At the same time, compliance with the Aarhus Convention on access to environmental information, public participation in decision-making and access to justice is required for all EU Member States and the EU itself – all of which are party to this Convention.