The Information Technology Infrastructure Library (ITIL) is readily available for establishing the best practices, reengineering and improving the IT service support process. However, the ITIL framework only provides recommendations, and a company needs to explore a methodology for improving the IT service support process and adopting the best guidelines of ITIL framework. To this end, this chapter investigates upon how to apply the ITIL framework can be used for evaluating the current IT service support process and its reengineering. A set of Key Performance Indicators (KPI) were established which are monitored by a decision support system (DSS) for triggering on-going reengineering of IT service support process. A case study methodology is used for an effective reengineering of IT service support process. This chapter focuses on implementing the ITIL guidelines at an operational level, improving the service desk, incident management, problem management, change management, release management, and configuration. It also focuses on implementing the ITIL guidelines at a tactical level, improving the service level management, capacity management, IT service continuity management, service availability, and security management. The chapter describes a methodology and an experience in implementing process reengineering techniques following ITIL framework.