This volume contains the invited papers of the Spring meeting of the Arbeitskreis Festk"rperphysik of the Deutsche Physikalische Gesellschaft, which has been held in Regensburg in the period March 23 - 27, 1998. The meeting has been attended by more than 2800 participants from all areas of solid state physics and other areas of physics as well since this time it has been organized together with the yearly general meeting. The invited and plenary talks as well as the numerous symposia reflected most recent developments in physics. This book covers the current status of the fileds and shows the excitement which has been felt by the speakers when presenting their results.