The emergence of heterogeneous teamwork that includes humans and Intelligent Virtual Agents (IVAs) represents a dynamic response to the fast growing usage of Virtual Environments (VEs). However, a key challenge is to transfer our knowledge about human-human teamwork to humans-IVA team-work. Trust and commitment are important elements in building strong human relationships. In the case of successful teams, trust and commitment to a shared goal and to one another are essential. This paper aims to investigate the impact of multimodal communication on the development of human trust in IVAs. An-other aim is to study the effect of trust on commitment and consequently hu-man-IVA team performance. The results from two studies involving a collabo-rative activity showed a significant positive relationship between trust and commitment. Moreover, the results indicated that human commitment tends to improve team performance.