The main purpose of this thesis has been to study the change agent’s role in accelerating sustainability in the construction sector. A case study was conducted in a large construction company (~9000 employees) with an ambitious sustainability profile. The research started by obtaining an understanding of organizational change, the change agents’ role and how change agents can be organized. The research then proceeded by studying whether there are practices among change agents leading to sustainable transition and how. Data was collected in a single case study through semi- structured interviews with four change agents, their director and one receiver of the change efforts.  How do change agents in a construction company, organized in a dual operating system, overcome change resistance in the line organization to accelerate sustainability?  The answers to the research question where that the change agents are the key persons of driving the transformational change effort in the studied company. They operate differently depending on situation and task, with no formal job description, requiring a high grade of personal strive. They have no formal responsibilities and few recourses, resulting in an importance of ability to influence others to take necessary decisions to change towards sustainability. They focus on building and maintaining relations with key persons in the line organization and prefer to be involved early in the projects. They spend time to train and engage in sustainability questions. They use their colleagues and fellow experts in the parallel organization to share competence, expertise and experience.  This study shows that change agents’ working in a dual operating system has been implemented with success in Company X. A successful dual operating system should include a larger unit of agents that gives them support and help from each other in their strive for change in any area of choice. When implementing the dual operating system, it should be considered that if the role definition is wide, creativity is stimulated among the change agents, making them develop new methods for implementing sustainable change. Furthermore, these best practices identified could be used for future change agent role definitions.  Even though change resistance exists in different forms, proactive prevention of resistance as have been done in Company X, seems to facilitate the change effort. As a result, the interviewees did not particularly experience change resistance. For future research, the case study could be expanded to include more respondents to study each area deeper and be able to confirm the best practices and the main challenges. It would be of interest to identify a company in a different sector that has implemented change agents and a dual operating system and perform a similar case study to identify any sector-specific differences. Some interviewees at Company X described there was an ongoing process on the job descriptions of the change agents. After the implementation of the updated job descriptions, it could be of interest to study changes in volunteerism and creativity among the change agents. Another aspect for further studies would be company size. Smaller companies with less management recourses probably must operate different and those differences would be interesting to understand further. Lastly, future research could study outcome of change effort using change agents in a dual operating system compared to change agents in the original organization.