This Research Handbook presents a comprehensive overview of the significance of systems theory for analysing law in modern society. Expert contributors examine key theoretical developments and core approaches to systems theory, illustrating the strengths of this transdisciplinary theoretical framework across research fields and areas of law. Chapters cover a range of areas of law that this approach can be applied to, including constitutional law and constitutionalism, contract law, environmental law, social work and labour law. The Research Handbook draws on detailed case studies to investigate how this theoretical framework can be used in diverse contexts, exploring human rights, hate speech, climate change governance and corruption through this lens. It also highlights the role of systems theory across technology and business, from artificial intelligence and cryptocurrencies to illegality in organisations, the regulation of risk and investment arbitration tribunals. This forward-looking Research Handbook will be valuable to students and scholars of systems theory and research methods in law, as well as jurisprudence more widely, as it provides an informative analysis of the latest research and thinking in this dynamic field.