There is consensus that the effective implementation of cross-functional teams is critical to new product success. However, such teams face particular challenges because of welldocumented barriers between functions. Furthermore, there is little evidence-based guidance for practitioners on how to achieve effective cross-functional teamwork. In order to address this gap, the literature on cross-functional teamwork was analysed to identify critical success factors. Using a heuristic team effectiveness model, these were categorized into six groups: task design, group composition, organizational context, internal processes, external processes and group psychosocial traits. Recent theory on group effectiveness has increasingly recognized the significance of a supportive organizational context, and this is particularly pertinent for cross-functional teams. Key success factors include strategic alignment between functions, a climate supportive of teamwork and team-based accountability. The findings are integrated into a diagnostic model which is intended to be of practical benefit to people designing, leading and facilitating cross-functional new product development teams.