An avalanche-like increase of research activities in the field was caused by the spectacular announcements and publications about the observation of nuclear fusion processes during the infusion of deuterium into metals. Though, the original claims by Fleischmann and Pons concerning the observation of macroscopic amounts of heat so far seem not to be approved in a quantitative manner by other groups, there are indications for the start of a new interesting field of research at the border between nuclear physics and solid state physics – investigations of nuclear fusion processes in condernsed matter. First conclusions drawn here about possible mechanisms of such processes have to be considered neither complete nor final.