ENChanges in the provisions of heritage protection significantly change the heritage policy and the conditions of and requirements for the emergence of new architecture on heritage sites. In order to analyze the conditions of and the possibilities for the insertion of new architecture and the reuse of existing buildings and their reconstruction in their historical environment, as well as the applicable requirements, restrictions and recommendations, an analysis of national and international legal documents was carried out, delving into two World Heritage Sites in Lithuania: The Vilnius Historic Center and the Curonian Spit. The article discusses the key international and national legal documents regulating the aspects of the emergence of new architecture in protected territories, highlighting the most significant principles of the legal regulation of the UNES CO World Heritage sites in Lithuania, which define the architectural, urbanistic, and aesthetic expression of buildings of contemporary architecture (new and reconstructed) in these territories.