One of the factors that seems to influence an individual’s effectiveness in requirements engineering activities is his or her knowledge of the problem being solved, i.e., domain knowledge. While in-depth domain knowledge enables a requirements engineer to understand the problem easier, he or she can fall for tacit assumptions of the domain and might overlook issues that are obvious to domain experts and thus remain unmentioned. The purpose of this thesis is to investigate the impact of domain knowledge on different requirements engineering activities. The main research question this thesis attempts to answer is “How does one form the most effective team, consisting of some mix of domain ignorants and domain awares, for a requirements engineering activity involving knowledge about the domain of the computer-based system whose requirements are being determined by the team?” This thesis presents two controlled experiments and an industrial case study to test a number of hypotheses. The main hypothesis states that a requirements engineering team for a computer-based system in a particular domain, consisting of a mix of requirements analysts that are ignorant of the domain and requirements analysts that are aware of the domain, is more effective at requirement idea generation than a team consisting of only requirements analysts that are aware of the domain. The results of the controlled experiments, although not conclusive, provided some support for the positive effect of the mix on effectiveness of a requirements engineering team. The results also showed a significant effect of other independent variables, especially educational background. The data of the case study corroborated the results of the controlled experiments. The main conclusion that can be drawn from the findings of this thesis is that the presence in a requirements engineering team of a domain ignorant with a computer science or software engineering background improves the effectiveness of the team.