Increased recognition of the importance of the social dimensions of learning has had a number of consequences for pedagogical theory and practice. Not least has been a blurring of the distinction between teachers and learners and, often associated with it, a reconceptualizing of the traditional classroom as a community of learners to which all members contribute. This new focus is reflected in many online learning environments, designed so as take maximum advantage of the opportunities for interaction provided by the Internet. Further, it is becoming increasingly common within such learning communities for participants to include software agents enacting a range of socially interactive roles ranging from fellow-learner to the more traditional tutor or instructor. This paper explores the extent to which these pedagogical agents can contribute to the effectiveness of online learning communities.