Enterprises and service providers are increasingly challenged with improving the quality of service delivery while containing the cost. However, it is often difficult to effectively manage the conflicting needs associated with dynamic customer workload, strict service level constraints, and service personnel with diverse skill sets. In this paper we propose an optimization model to provide recommended staffing levels in a complex service delivery system. The optimization model minimizes the total staffing related variable cost while considering the contractual service level constraints, the skills required to respond to different types of service requests, and the shift schedules that the service agents must follow. We describe how model-based decision making can be conducted using a combination of optimization and discrete event simulation techniques. We demonstrate the applicability of the proposed approach in a large IT services delivery environment. © 2011 IFIP.