This book is about longitudinal research in Human-Computer Interaction (HCI). Since the early 1980s much has been understood about the problems of novices learning new systems as well as the performance of expert users. However there is still a lot to discover about the transition from novice to expert and its implications for the design of systems. For instance: - How long does it take to become expert? - Does early experience of a system have any effect on subsequent flexibility? - How can flexibility and long term learning be promoted? - Are there strong constraints that should be taken...