Fiber spaces, connections and Yang-Mills fields -- A geometric introduction to Yang-Mills-equations -- Symmetry as a clue to the physics of elementary particles -- Topological excitations in gauge theories; An introduction from the physical point of view -- Particles, fields and quantum theory -- Monopole solitons -- Yang-Mills theory and Gravitation: A comparison -- The twistor description of linear fields -- Twistor techniques in gauge theories -- Simple pseudopotentials for the Kd V-equation