This is a collection of lectures and seminars delivered at the "Symposi- um on Particles and Fields" held at TUbingen University, West Germany, th from June 20 to July Pt, 1977, on the occasion of the University's sooth anniversary. We were very fortunate that so many excellent colleagues from Europe and the U. S. contributed their ideas to this meeting, whose main pur- pose ist was to cover a brod spectrum of the various aspects in the current development of particles and fields, rahter than to focus on a single subject. It was interesting to see source-, quark-, and string- people side by side attacking the very same unsolved problems in particle physics. Exchange of ideas and techniques between the diverse representatives of field- and particle physics was the principal goal of the meeting. Last not least, we are most grateful to the President of our University A. Theis, and his assistant, H. E. Lang, for the generous support that enabled us to make this symposium a profitable and pleasant experience for all of us.