This article provides a detailed examination of the theory of intertextuality and the concept of intertextual relations, which were formulated in 20th -century literary studies. The theory of intertextuality interprets a literary text not as an independent and closed system, but as an open semantic field intrinsically linked with other texts. According to this approach, each text absorbs elements of previous texts, reworks them, and presents them in a new context. Thus, intertextuality manifests as one of the fundamental principles of artistic creation, as it enriches the semantic layers of the text and expands its interpretive possibilities. The article considers the concept of dialogism as a central tenet of intertextuality. Furthermore, the article theoretically analyzes the primary devices of intertextuality: citati on, allusion, reminiscence, and text -within-a- text. Through citation, an author incorporates specific passages from other texts into their work, thereby reinforcing an idea. Allusion, in contrast, refers to another text, event, or historical source through a subtle or overt reference. Reminiscence is the conscious or unconscious adaptation of a prior literary or cultural experience to a new text. The text -within-a-text model, particularly in postmodern literature, creates complex compositional layers in a work and draws the reader into an intellectual game with the text. In postmodern literature, intertextuality constitutes not only the relationship between texts but also a mechanism for intellectual play between the text and the reader. Authors reinterpret historical, religious, or literary texts, updating them in an ironic or playful style, thereby expanding the semantic potential of the text and transforming the reader into an active interpreter. In conclusion, the theory of intertextuality enables the stu dy of a literary text as a multi -layered and open system that is integrally connected with other texts. Intertextuality, intertextual relations, dialogism, quotation, allusion, reminiscence, postmodern literature, text-within-text.