This book examines how private justice challenges the state's monopoly on adjudication, with a particular focus on today's digital contexts. The author contends that private interventions can be legitimate expressions of justice rather than threats to it, and argues for a nuanced approach. This applies when such interventions respond to genuine injustices and meet the criteria of suitability, necessity and proportionality while respecting fundamental ethical boundaries. By proposing a framework for private justice defence, the book explores how this stance could bridge the gap between public and private justice systems, fostering greater collaboration between citizens and the state. By acknowledging the role of private adjudication in rectifying injustices, the book advocates a legal landscape that empowers individuals to act in the service of justice, while upholding core principles of fairness and cooperation. The book will appeal to scholars of legal theory and law and technology.