The collective monograph is devoted to the study of the system and hierarchy of sources of law in various national legal systems: Russia, Bulgaria, Armenia, Belarus, Kyrgyzstan and Kazakhstan. The team of authors from eight countries of the world analyzes the system of formal and informal sources of law, touches upon the role of legal customs, judicial practice, acts of constitutional control bodies, principles of law, legal doctrine, sources of international law in legal regulation. The team of authors pays special attention to the ratio of different sources of law, the rules for resolving conflicts between them, as well as the experience of implementing the laws of Bulgaria and the CIS states on regulatory legal acts. The book will be of interest to scientists, practitioners, teachers and students of law universities.