Note: This book is available in several languages: Chinese, English. This is the first book to provide a coherent view and guidance for using the Six Sigma approach successfully in IT service organisations. It particularly aims to merge ITIL and Six Sigma into a single approach for continuous improvement of IT service organisations. Six Sigma provides a quantitative methodology of continuous (process) improvement and cost reduction, by reducing the amount of variation in process outcomes. The production of a product, be it a tangible product like a car or a more abstract product like a service, consists of a series of processes. All processes consist of a series of steps, events, or activities. Six Sigma measures every step of the process by breaking apart the elements within each process, identifying the critical characteristics, defining and mapping the related processes, understanding the capability of each process, discovering the weak links, and then upgrading the capability of the process. It is only by taking these steps that a business can raise the ‘high-water mark’ of its performance. IT is now a fundamental part of business and business processes; this book demonstrates how IT can be made to work as an enabler to better business processes, and how the Six Sigma approach can be used to provide a consistent framework for measuring process outcomes. ITIL defines the ‘what’ of Service Management; Six Sigma defines the "how" process improvement; together they are a perfect fit of improving the quality of IT service delivery and support. The Six Sigma approach also provides measures of process outcomes, and prescribes a consistent approach in how to use these metrics.