The paper explores the essence and structure of public order as a general principle of every legal and social system, as well as a clause in international private law. The complexity, dynamics and importance of public order are described in this paper. The author emphasizes that public order in the broadest sense entails not only mandatory provisions, but also moral rules, accepted standards and judicial practice. This institute covers crucial social values, institutes and actions of public bodies. Public order has at least two objectives: 1) protection - public order protects human rights and freedoms as well as social community, 2) regulation of social processes, especially of public services. For this reason it is not possible to reduce public order to restrictions and/or orders. Finally, the author introduces the most important characteristics of public order and classifications of this institute.