This thesis explores the individual and group processes that occur in qualitative group model building, mostly using applied research in New Zealand government departments. System dynamics is an approach to understanding the behaviour of systems over time. Originally, system dynamics practitioners would advise corporate managers on business decisions. To improve the adoption of these proposed interventions, some practitioners experimented with involving client groups in the modelling process, now commonly referred to as "group model building". Researchers not only discovered that group model building supports client commitment to implementing the conclusions of the modelling process, but also noted a range of intrapersonal and interpersonal changes in participants. However, group model building literature remains unclear on what these changes are, and how they occur. In Chapter 2, a literature review explores what intrapersonal and interpersonal factors predict effective strategy implementation. An observational study was conducted, and suggests that group model building workshops can have a positive impact on the intention to implement strategy. Several cognitive biases were proposed to explain this effect. Group model building literature claims mental model change and mental model alignment as outcomes, but it is not clear that the evidence supports these claims. Mental models are relatively enduring structures, and previous studies only evaluate changes observed immediately after the group model building workshop. Chapter 3 follows participants in four group model building workshops over a 12-month period. The results demonstrate that participants change their decision preferences through the workshop, and that without reinforcement these changes persist for 12 months, suggesting mental model change. Participants' preferences also become and remain more alike, suggesting enduring mental model alignment. Individuals whose mental models are more aligned are more likely to agree, and this can be an important outcome where decision groups are expected to build shared understandings over time. The I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the General Award Rules of The University of Queensland, immediately made available for research and study in accordance with the Copyright Act 1968.