This study deals with collective memory as a cognitive reference that contributes to shaping the design decision in interior design, distinguishing itself from contemporary literature that focused on cognition and reflective thinking without giving sufficient attention to the social and cultural roots; and the study aims to build a theoretical framework that explains the relationship between them, through analyzing the path in which experience transfers from society to design knowledge. The study adopted the critical analytical method through reviewing and analyzing the founding literature in the fields of collective memory, cultural memory, tacit knowledge, design knowledge, and reflective thinking, then reconstructing them into an explanatory conceptual model. The findings reached that collective memory does not affect the design decision in a direct way, but rather its effect is embodied through a cognitive chain that passes through cultural memory, then tacit knowledge, then design knowledge, leading to reflective thinking; as it proved that design knowledge represents a reorganization of previous social and cultural experiences, as the study recommends expanding the theoretical understanding of the designer's sources of knowledge, and adopting the proposed conceptual model as an integrated explanatory framework in interior design research. It also calls for conducting future applied studies to test this model, and measure its effectiveness in different design contexts and compositions............. Keywords: ............Collective Memory, Cultural Memory, Tacit Knowledge, Design Knowledge, Design Decision, Interior Design.