The great success of the experimental research on elementary particles and their qualities during the last years suggests giving a summary of the present situation also in the theoretical description of this important branch of physics. In spite of the precarious situation in this field of theoretical physics I believe I can fully account for this choice and must see that the number of participants and the general interest justify my opinion. In organizing the proceedings it was our prime concern to reduce the delay in editing and also keep down the price. This was possihle only through the assistance of the Springer-Verlag who chose photomechanical method working quicker and cheaper. Therefore we apologize for any mistakes and errors that may occur in the text and formulae. I am very indebted to my secretary, Miss A. SCHMALDIENST and one of my assistants, Dr. H. KÜHNELT, who did an the typing and correcting of the manu­ scripts with great patience and knowledge.