What does it mean when we say the international rule of law (IROL)? How does harmonization contribute toward the development of the IROL? When we refer to harmonization, what do we mean by it? What does it mean when we refer to the harmonization of public and private international laws? Do public and private international laws play different roles toward the IROL and harmonization? We address these questions in this chapter and try to understand their significance. Harmonization of international law can lead to the growth of the IROL. With this premise, the chapter aims to examine the concept of IROL and the harmonization of international law. The chapter also highlights the convergence of public and private international laws through scholarly work. The final part of the chapter addresses various elements of IROL and harmonization. It also analyzes the application of the principle of justice to both the international rule of law and the harmonization of international law.