The Chief of Staff (CoS) plays a central and often decisive role throughout the M&A process. Already in the preparation phase, the CoS acts as a coordinator between the management team, business areas, and external advisors. The CoS is responsible for collecting and structuring information, ensuring that the due diligence process covers both financial, legal, and cultural aspects, and identifying risks and opportunities early on. During the actual negotiation, the CoS is often the one who keeps the communication together, prepares the decision-making materials, and ensures that all parties are informed about the status and next steps. After the signing of the agreement, the CoS is the key person in planning and driving post-merger integration (PMI), focusing on creating a common understanding of goals, structuring the integration process, and ensuring that change management and communication work. In Swedish organizations, where consensus and flat hierarchies are the norm, CoS is particularly important for creating engagement and buy-in among employees and trade union partners. The role requires both strategic overview and operational agility, as well as the ability to navigate complex and changing environments.