The study reported in the present paper forms part of an ongoing project regarding the teaching of functions in undergraduate courses at three Swedish universities. The theoretical framework underlying the project is Sfard’s commognitive theory. In the present study, three lectures in calculus from two different universities are analyzed, focusing on the characterizations of the function concept presented by the discursive practices of the teachers. All three teachers are found to make extensive use of the principle of variation, but differences are found for instance in the emphasis put on different realizations of functions, and on the role of domain and range. Also, according to the type of content of the lectures, differences between more process-oriented and more object-oriented discourses of functions can be seen.