Jahn-Teller effect and vibronic interactions: General theory.- Recent Developments in the Jahn#x2013;Teller Effect Theory.- Electronic Degeneracy and Vibrational Degrees of Freedom: The Permutational Proof of the Jahn#x2013;Teller Theorem.- Group-Theoretical Analysis of Jahn#x2013;Teller Systems.- Spin#x2013;Orbit Vibronic Coupling in Jahn#x2013;Teller and Renner Systems.- Vibronic Coupling Constant and Vibronic Coupling Density.- A New Method to...