During an interaction, participants demonstrate interpersonal coordination by adapting to each other. Coordination can be marked by the reciprocity of behaviours and their similarity. A wide variety of cues, such as multimodal behaviours, linguistic cues, politeness strategies, beliefs, social attitudes, and emotions, may be involved. Adapting the multimodal behaviours of a socially interactive agent to the behaviours of its human interlocutors can promote engagement, build rapport and trust, and support the learning process. In this talk, I will present some of the work we have explored. I will describe the computer models of the different adaptation mechanisms and the experimental studies we have carried out to validate them.