The subject matter of the research and its relevance The subject matter. In the present paper one of the inter-branch law institutes namely – the oath is being under discussion. The treatment of the problem embraces the development of law from time honored stages up to the present state. Within the period the law terms has changed considerately and the process is still in progress, especially in the sphere of the implementation of its functions. In the given paper the objects of research are the historical and native Lithuanian sources; i.e. the norms of national, international legal acts and the acts of other states in which the oath institution is called upon, as well as the Lithuanian law doctrine dealing with this problem. The general approach to the research of the juridical Oath Institution and its social significance has a long standing tradition in Lithuania. The cognition of the concept of the oath is an organic element of the law doctrine, as an integral formation, however has never yet received a deeper research either in legal norms or in theory. The given paper is an attempt to reveal the juridical and social essence of the oath, its evolution and transformation into a really meaningful juridical regulation of values and its fitting functions. It ought to be a concentration of the fundamental values stated in the Constitution and at the same time – an instrument of the assurance of their implementation. Rephrasing prof. A. Vaišvila „when explaining law (in this case – law as a concentrated expression of law) it is not sufficient to state that law (in this case – the oath [singled out by the researcher] as a rule of behaviour (a matter of form). It is important to reveal its essence, i.e. its correlation with social interests, whose expression this particular rule of behaviour is“. The expression of the rules of behaviour functioned by word of mouth before the written law emerged. Nevertheless, it preserved essential features for its successful implantation. These features arouse more than one conceptual doctrine question the answer to which has become a permanent law scientific research problem. Thus, the primary theoretical problem of the given paper is the analysis of the main oath features and its correlation with the social environment, the localization of the oath in the law system and finally the formulating of the definition. Further on, it is an attempt to reveal the significance of the values guarded by the oath, and to try to prove that the two factors are mutually supportive interdependent. At the same time the aim is to show that between the undertaken commitments – the efficiency and the oath institution there is an organic bilateral relationship. It is quite evident that the current situation in the state does not provide prerequisites to state de facto that the oath institution is omnipotent. This encourages not only looking deeper into the content of the oath institution but also searching for new means to ensure the efficiency of the analyzed institution. The attempt to work out objective and rational means of eliminating the above stated drawbacks encouraged to abstract the following theoretical problems: social context and the necessity to form a relationship regulating organ, i. e. the Institute of the Oath. The Institute’s function is the application of formal and content criteria, the sufficiency of legal reglamentation and Institute supervision (control) efficiency and sufficiency in Lithuanian law.