Since the need for a third edition of this book has arisen, we have endeavoured to improve and extend it in several ways. At many places small changes were made, misprints have been corrected, and references have been added. In Chap. 5 new theoretical and experimental results on the Lamb shift in heavy atoms and on the anomalous magnetic moment of the muon are reported. We have also added a number of new topics in Chaps. 3, 5, and 7 in the form of examples and exercises. Example 3. 19 contains a detailed treatment of electron-positron pair production in the collision of a high-energy photon with a laser beam. This is supplemented by Exercise 3. 20 where a closed solution of the Dirac equation in the field of a plane wave is derived. Furthermore, Example 5. 4 on the running coupling constant in QED and Example 7. 6 on the supercritial point charge prob lem have been added. Finally, Example 7. 8 treats the birefringence of the QED vacuum in a strong magnetic field. We thank all colleagues and readers who have informed us about misprints in the book and are grateful to the team at Springer-Verlag for expertly handling the preparation of this new edition. Frankfurt am Main, Walter Greiner August 2002 Joachim Reinhardt Preface to the Second Edition The need for a second edition of our text on Quantum Electrodynamics has given us the opportunity to implement some corrections and amendments.