This chapter explores the foundational principles and core functions of law, explaining how they shape the nature, structure, and purpose of legal systems. It begins by defining principles of law as overarching ideas that guide the formation, interpretation, and application of legal norms, emphasizing their role in ensuring freedom, justice, and order in society. General principles such as social freedom, justice, democracy, humanism, equality, legality, and responsibility, are presented as universal standards embedded in both national and international law. The chapter also introduces cross-branch (interdisciplinary) and branch-specific principles, illustrating how legal coherence is maintained across diverse areas like criminal, civil, and procedural law. A key discussion focuses on the controversial yet increasingly accepted role of legal principles as sources of law, especially in filling gaps where written norms are absent. Drawing comparisons between domestic and international legal systems, the chapter highlights the growing recognition of principles in legal practice. Finally, it outlines law’s two primary social functions: regulatory (structuring social relations) and protective (guarding society against harmful acts). Together, these principles and functions underscore law’s dynamic role in promoting societal progress, legal certainty, and individual dignity particularly relevant for legal reform in post-Soviet states.