Experimental evidenees for non vanishing neutrino masses are now very eon­ vincing. In the third English edition we have rewritten the paragraphs in which, in the previous edition the question of the neutrino mass has been left open. We have mueh appreciated the diseussions with Stephan Sehönert (Heidel­ berg) on the new results of the neutrino oseillations and their interpretations. We would like to thank Martin Lavelle (Plymouth) for the translation of the newly written paragraphs and Jürgen Sawinski (Heidelberg) for the exeellent work he has done in reformatting the book. Heidelberg, May 2002 Bogdan Povh Preface to the Second Edition The second English edition has been updated from the fifth edition of the original German text. The principal addition is a chapter on nuclear ther­ modynamics. We consider in this chapter the behaviour of nuclear matter at high temperature, how it may be studied in the laboratory, via heavy ion experiments and how it was of great importance in the initial stages of the universe. Such a phase of matter may be described and interpreted using the tools of thermodynamics. In this way a connection between particle and nuclear physics and the currently exciting research areas of cosmology and astrophysics may be constructed. We would like to thank Martin Lavelle (Plymouth) for the translation of the new chapter and for revising the old text and Jürgen Sawinski (Heidelberg) for the excellent work he has done in reformatting the book.