Intertextuality is a prominent feature of academic writing, and the ability to use sources effectively and appropriately is an essential skill which novice writers must acquire. It is also a complex skill, and student performance is not always successful. It is presumably beneficial for students to receive consistent messages about what source use is and is not appropriate, but some evidence suggests that university teachers and other gatekeepers may fall short of this consistency. This paper reports the findings of semi-structured text-based interviews aimed at understanding the basis of teacher attitudes and responses to intertextuality in academic writing. Teachers who were asked to evaluate the same examples from student texts differed in their judgments about whether the examples were appropriate, and provided different types of explanation for their judgments. These explanations enable us to develop a four-part typology of intertextuality which allows analytic discussion of differing judgments. The implications both of the teacher judgments and of the typology for second language writing instruction are discussed and an assessment of the relevance of our findings for the theme of this special issue is provided.