The modern existence of Russian families is characterized by a variety of lifestyle forms. The changing family landscape, which includes a range of blood and non-blood relatives and partners, expands the understanding of this institution, leading to broader definitions of the family and its boundaries. The purpose of the article is to analyze the dynamics of young people’s representations about family boundaries. The article attempts an interdisciplinary synthesis of theoretical and practical knowledge, namely the application of semiotic analysis in sociological research. The theoretical and methodological basis of the study Yu.M. Lotman. The empirical base consisted of data from three studies conducted using a similar methodology: 2007 (n=213), 2017 (n=132), 2023 (n=113). Using the concept of “significant family member”, the mobility of family boundaries is revealed. The respondent’s partners – young people, common-law spouses – “moved” from the periphery to the core of the family. The greatest changes occurred in the structure of family ties. The concept of S.I. Golod made it possible to theoretically substantiate the transformation of ideas about the family and its boundaries. Yu.M. Lotman's approach to the analysis of the phenomenon of borderliness complemented the ideas about the essence and functions of the boundaries of the family sphere and made it possible to theoretically interpret their dynamics. Interdisciplinary synthesis of sociological and semiotic knowledge when studying the boundaries of the family sphere seems promising.