Genre analysis of texts has always been significant. The current study aimed at investigating intertextuality considering cultural variations and differences in students' discourse communities. Social studies, philosophy, and biology were chosen as the representatives of social sciences, humanities and sciences. Tehran University, one of the most prominent and oldest universities in Iran, was chosen as the source of the theses. From each discipline, eight theses were chosen randomly and the organization of the introductions was analyzed according to Samraj's revised model of Swales (2008). Next, a comparative and contrastive analysis was performed between the results obtained from this study and the ones obtained from Samraj's (2008). The results indicated that social studies and biology introductions were quite similar and followed the traditional format of thesis writing whereas philosophy introductions were different as they had a more topic-based structure.