This article explores service learning via the lens of activity theory. Through this lens, it is identified as a form of "boundary work" in higher education, with educators identified as "boundary workers". Drawing on the data from a recent study, this paper analyses service learning as an often contradictory and tension-filled practice. The "expanded community" and "dual but interrelated object" in the service learning activity system result in many tensions for students and community members alike. This in turn poses significant challenges for boundary workers, and ultimately for the university. The paper concludes by arguing that in order to encourage and value service learning, we need to acknowledge the (new and different) knowledge, values and skills required for playing the role of boundary worker in (boundary) practices such as this. (Contains 1 figure and 3 notes.)