With so many professionals online and relying on the Internet to perform daily operations, application performance has become vital to the success of an eBusiness solution.  In an effort to ensure success, many companies have developed tools and methodologies to test and tune applications for performance.  These tools and methodologies have focused around optimizing system metrics, rather than optimizing user experience.  The User Experience, Not Metrics Series of articles will address topics related to determining true user experience and application performance tuning using Rational Suite TestStudio coupled with a proven approach to engineering end-to-end system performance that focuses on end-user experience.This introduction is intended to provide the high-level concepts and terminology used throughout the User Experience, Not Metrics Series of articles.