This study examined the development and dynamics of trust in project teams and explored the relation with cooperation, monitoring and team performance. Two types of teams were distinguished at the start of the projects: low prior social-capital teams (teams composed of members that have no previous history in working together and are not acquainted or friends with one another); high prior social-capital teams (teams composed of members that have worked together previously, are acquainted or friends with each other). A longitudinal approach provided an opportunity to study trust dynamics in the course of the projects. Data from 79 project-research teams (315 master's students) was collected longitudinally, with measurement moments at the beginning, middle and end of the project. Independent team performance ratings were obtained for each team. Significant differences were found in relation to trust-building between high and low prior social-capital teams. High prior social-capital teams reported systematically higher levels of trust than low prior social-capital teams throughout the project. These differences had implications for the level of monitoring, cooperation and team performance. © The Author(s), 2009.