ENThis article explores the problems of understanding the meaning of the acquis communautaire in EU law system. The problems of application of the criterion «acquis communautaire» during the process of the integration of the Republic of Latvia and the Republic of Lithuania are analyzed in the article. The acquis communautaire is the body of rules and regulations, which the EU has introduced to new countries. The aquis were split into 31 chapters for Latvia and Lithuania. The chapters include areas such as labor law, competition policy, economic areas, agriculture, consumer and health protection. The cooperation in the field of justice and home affairs are the most necessary regulations in EU law during the integration. The adoption of the acquis communautaire means that Latvia and Lithuania have to adapt their enterprises and main infrastructure to respect EU norms and standards en general. Applying to the original law of the EU, the law of Latvia and Lithuania and the theory of European law, the author states the peculiarities of its using in the system of law of Latvia and Lithuania in general and in incorporation of this criterion in different spheres of law. The article concludes that in spite of absence the legal definition of acquis communautaire in the original law of the EU the process of implementation of this criteria was quiet fast in Baltic States. Analysis of the selected spheres of law (labor law, law of moving the capitals, Schengen law) in Lithuania and Latvia illustrates that the implementation of acquis was quiet necessary during the integration because the legal meaning of many definitions, legal regulatory were different. [From the publication]