Plagiarism and collusion are significant issues for most lecturers whatever their discipline, and to universities and the higher education sector. Universities respond to these issues by developing institutional definitions of plagiarism, which are intended to apply to all instances of plagiarism and collusion. This article first suggests that plagiarism and collusion are related instances of the desirable phenomenon of intertextuality, but which are defined as transgressive, that is, intertextuality that crosses a boundary defining relationships that are inappropriate in a specific context. The article then goes on to show, through interviews with lecturers in a variety of disciplines, that lecturers' interpretations of inappropriate or transgressive intertextuality vary for reasons including the expectations and practices of the discipline. The article suggests that transgressive intertextuality needs to be defined according to the disciplinary expectations and that a single institutional definition may be inadequate to defining varying disciplinary perspectives. (Contains 2 notes.)