This chapter begins with a brief overview of the UNCLOS dispute settlement system established under Part XV UNCLOS. It then provides a conceptual framework for understanding what is meant by ‘development of the law’ by international courts and tribunals in order to set the stage for an analysis of the development of the law of the sea in the subsequent chapters. The chapter suggests a working definition of the term ‘development of the law’ and explains the ways in which international courts and tribunals ‘develop the law’. In the course of doing so, the chapter also explores the role of legal reasoning in the assessment of the contribution of judicial decisions to the development of international law.