This book analyses in a comprehensive manner the phenomenon of 'public interest' in different areas of law, both public and private. The term 'public interest' can be found in a wide range of legislation and it is used extensively in judicial practice and public administration. Yet, it has received surprisingly little attention in academia. As a result, it is used for various, often contradictory purposes. Justifications for its application are rarely convincing and the concept is often confused with similar legal institutions such as state interest, societal interest and public welfare, which, however, serve quite different purposes. Further to the relevant public being defined, the weight of public interest in case of conflict with other considerations will be examined and the legal consequences of its breach (e.g. nullity, damages and penalties) considered.The book's objectives are therefore manifold. First and foremost, it aims to provide a definition of the notion of public interest and to determine its main attributes, particularly against the background of the notion of private interest. In order to achieve this, the concepts philosophical underpinnings will be outlined, as will its historical developments and its application in different times and socio-economic conditions. Consequently, the book will assist in applying the concept of public interest with a clear understanding of its substance, normative function and its relationship to other relevant legal institutions. The book focuses on the concept's application across the spectrum of legal disciplines ranging from constitutional and administrative law to corporate and insolvency law, from criminal law to environmental law, and from competition law to labour law. In order to provide concrete examples of legislative and judicial practice, the book analyses three jurisdictions in particular Austria, the Czech Republic and the European Union.This book is not only an important addition to legal scholarship but, importantly, contributes to the improvement of decision-making processes at all levels of government. It will be of interest to scholars, practicing lawyers, judges and officials in public administration alike.