The European Commission (the Commission) employs more than 22,000 officials who provide administrative services to the European Union. In 2003, the Commission introduced a performance appraisal and promotion system based on points that the officials earn each year. In 2006, the Commission realized that the system needed to be revised. To support the review process, the Commission invited tenders for a project to develop simulation models that it could use to project the future performance of the existing system. A team from Lancaster University won the bid and subsequently worked closely with Commission officials to develop a new system. In 2009, the stakeholders in the Commission's performance appraisal and promotion system agreed to implement the improved system. The simulation model is unusual in the field of manpower planning because it models the consequences of appraisal-system rules. It uses novel, accurate, and efficient sampling techniques that are based on regression models of the underlying relationships in the data. The model was a crucial part of renegotiating the appraisal and promotion system and implementing a new system.