The development of an information system success instrument is central to the development of the field of MIS. Research progresses by following a cyclical process of theory development and theory testing. The definition of an information system success construct underlies the development of a cumulative MIS research tradition by allowing for cross study comparisons, replications and providinng an important link in the scientific research cycle. This text focuses on insights and developments related to system success, comparisons of system success instruments, validation of system success measures, and new and improved measures of systems success. It is intended to provide researchers and professionals with a comprehensive reference for understanding and measuring systems succss.