This chapter examines the internal system and structure of law, presenting it as an organized hierarchy of norms, institutions, and branches that regulate social relations. At its core is the legal norm, defined by a three-part structure: hypothesis, disposition, and sanction. These norms are classified by function (prohibitive, obligatory, empowering, and incentive) and by their role in either substantive or procedural law. Legal institutions are collections of norms regulating specific social relations, while branches and sub-branches organize these institutions into broader legal domains. The chapter distinguishes between public and private law, showing how each addresses different societal and individual needs. It also clarifies the difference between the legal system, i.e., the substance of law, and the legislative system, i.e., its formal expression. International law is explored as a unique, decentralized framework based on sovereign equality and mutual consent. The chapter concludes with a breakdown of how law operates in practice through four forms of implementation: compliance, execution, use, and application, demonstrating how legal norms are translated into real-world behavior.