In a comprehensive approach this book covers the end-to-end process from request management to change management, error management and migration management to acceptance testing and final data clean up. It is based upon nearly twenty years of experience in tests, acceptance and certification, when introducing medium to large IT systems including complex software for administrations and industry in many countries. There exist a variety of methodologies with different characteristics having emanated from various schools and consultancies to support such activities. However, it is obvious that because of the diversity in organisational levels in companies the rigor of application of such methodologies quite often suffers with regard to more pragmatic approaches. In view of economic considerations this may be unavoidable. For this reason no new or consolidated methodology shall be presented but an approach oriented on practical criteria coming closer to reality and offering methods, which can provide assistance on a case-by-case basis.