The past meetings held under the auspices of the Austrian Ministry of Education and the successes and benefits derived from these lectures in former years have encouraged us to continue this year with a survey of high energy physics. The experimental side of this field has undergone such a great advancement that the evaluation of huge masses of data called for the theoretical physicist to develop new theories and to explain facts and connections which we have not been able to clarify up to the present. In spite of the precarious situation especially in the field of Elementary Particle Theories, the theoretical physicist is about to summarize the present situation and to give further impulses for thc progress of our knowledge in nuclear physics. Thus the results of the Sixth International Meeting in Schladming and the interest shown in it fully justify our endeavours in this direction. In organizing the publication of the proceedings we shall continue on the same lines as hitherto so as to reduce delays through editing to an absolute minimum and to offer the publication at a reasonable price. I am again grateful for the assistance of the Springer-Verlag whose photo­ mechanical method proved so süccessful. Nevertheless we wish to apologize for any mistakes that might have occurred in writing the text of formulae.